The interpretation timeline
Matthew 1:20 Douay-Rheims

But while he thought on these things, behold the angel of the Lord appeared to him in his sleep, saying: Joseph, son of David, fear not to take unto thee Mary thy wife, for that which is conceived in her, is of the Holy Ghost.

A.D. 397 – 1871 14 witnesses 25 excerpts

Patristic

before A.D. 750
397
A.D.
Ambrose of Milan Patristic
A.D. 339–397
“In this word appeared is conveyed the power of Him that did appear, allowing Himself to be seen where and how He pleases.”
“(in Luc. ii. 5.) Be not troubled that he calls her his wife; for she is not herein robbed of her virginity, but her wedlock is witnessed to, and the celebration of her marriage is declared.”
407
A.D.
John Chrysostom Patristic
A.D. 347–407
“Also observe the mercifulness of Joseph, that he imparted his suspicions to none, not even to her whom he suspected, but kept them within himself.”
“He did not appear so openly to Joseph as to the Shepherds, because he was faithful; the shepherds needed it, because they were ignorant. The Virgin also needed it, as she had first to be instructed in these mighty wonders. In like manner Zacharias needed the wonderful vision before the conception of his son.”
“But by saying, Be not afraid, he shews him to be in fear that he had offended God, by having an adulteress; for only as such would he have ever thought of putting her away.”
“He says, Fear not to take unto thee; that is, to keep at home; for in thought she was already dismissed.”
“Or, The Angel appeared to Joseph when he was in this perplexity, that his wisdom might be apparent to Joseph, and that this might be a proof to him of those things that he spoke. For when lie heard out of the mouth of the Angel those very things that he thought within himself, this was an undoubted proof, that he was a messenger from God, who alone knows the secrets of the heart. Also the account of the Evangelist is beyond suspicion, as he describes Joseph feeling all that a husband was likely to feel. The Virgin also by this was more removed from suspicion, in that her husband had felt jealousy, yet took her home, and kept her with him after her conception. She had not told Joseph the things that the Angel had said to her, because she did not suppose that she should be believed by her husband, especially as he had begun to have suspicions concerning her. But to the Virgin the Angel announced her conception before it took place, lest if he should defer it till afterwards she should be in straits. And it behoved that Mother who was to receive the Maker of all things to be kept free from all trouble. Not only does the Angel vindicate the Virgin from all impurity, but shews that the conception was supernatural, not removing his fears only, but adding matter of joy; saying, That which is born in her is of the Holy Spirit.”
Source
420
A.D.
Jerome Patristic
c. A.D. 347–420
“But we are not to think that she ceased to be betrothed, because she is here called wife, since we know that this is the Scripture manner to call the man and woman, when espoused, husband and wife; and this is confirmed by that text in Deuteronomy, If one find a virgin that is betrothed to a man in the field, and offer violence to her, and lie with her, he shall die, because he hath humbled his neighbour’s wife. (Deut. 22:23.)”
Source
430
A.D.
Augustine of Hippo Patristic
A.D. 354–430
“(Enchir. 38.) But shall we therefore say that the Holy Spirit is the Father of the man Christ, that as God the Father begot the Word, so the Holy Spirit begot the man? This is such an absurdity, that the ears of the faithful cannot bear it. How then do we say that Christ was born by the Holy Spirit, if the Holy Spirit did not beget Him? Did He create Him? For so far as He is man He was created, as the Apostle speaks; He was made of the seed of David according to the flesh. (Rom. 1:3.) For though God made the world, yet is it not right to say that it is the Son of God, or born by Him, but that it was made, or created, or formed by Him. But seeing that we confess Christ to have been born by the Holy Spirit, and of the Virgin Mary, how is He not the Son of the Holy Spirit, and is the Son of the Virgin? It does not follow, that whatever is born by any thing, is therefore to be called the son of that thing; for, not to say that of man is born in one sense a son, in another a hair, or vermin, or a worm, none of which are his son, certainly those that are born of water and the Spirit none would call sons of water; but sons of God their Father, and their Mother the Church. Thus Christ was born of the Holy Spirit, and yet is the Son of God the Father, not of the Holy Spirit.”
Source
450
A.D.
Peter Chrysologus Patristic
c. A.D. 380–450
“As her betrothed husband also he is admonished not to be afraid; for the mind that compassionates has most fear; as though he were to say, Here is no cause of death, but of life; she that brings forth life, does not deserve death.”

Medieval

c. 750 – 1100
856
A.D.
Rabanus Maurus Medieval
c. A.D. 780–856
“How the Angel appeared to Joseph is declared in the words, In his sleep; that is, as Jacob saw the ladder offered by a kind of imagining to the eyes of his heart.”
“Or, to take her, that is, in marriage union and continual converse.”
908
A.D.
c. A.D. 841–908
“Because Joseph was minded, as has been said, to put Mary away privily, which if he had done, there would have been few who would not rather have thought her a harlot than a virgin, therefore this purpose of Joseph was changed by Divine revelation, whence it is said, While he thought on these things.”

Scholastic

c. 1100 – 1500
1256
A.D.
Thomas Aquinas Catholic
1225–1274
“"And she shall bring forth a son." Here he foretells the service that Joseph will render to the child now born, and he does three things: first he foretells the Virgin's childbearing; second he shows in advance the service to be rendered by Joseph himself to the child, when he says "and you shall call his name"; third he discloses the name imposed upon the child himself, when he says "Jesus." He says therefore "she shall bring forth." Thus she conceived of the Holy Spirit indeed first, but she shall bring forth a son. He does not say "to you," because he himself did not beget the child. In Luke 1:13 it was said to Zachary: "your wife shall bear you a son," because Zachary himself begot him. Or he does not say "to you" for this reason, that it may be shown that he was born for all: not only to you, or to her, shall she bring forth a son, but to the whole world; Luke 2:10: "behold, I announce to you a great joy, for there is born to you this day a Savior, who is Christ the Lord, in the city of David," and so on. But because Joseph could say: thus she herself conceived of the Holy Spirit, and shall bring forth a son, what then is this to me? In nothing am I necessary to him. Therefore he adds Joseph's own service: "you shall call his name." It was the custom among the Hebrews, and is so today, that on the eighth day they circumcised the child, and then imposed a name upon him; and this was done through Joseph: hence in this work he was the minister. Hence it is said to him "you shall call"; it is not said "you shall impose," because it is already imposed upon him; Isaiah 62:2: "a new name shall be called to you, which the mouth of the Lord has named." "Jesus" — this is the name imposed by God. And he gives the reason: "for he himself shall make his people safe," whom he acquired for himself by his own blood, that is, his people. Daniel 9:26 it is said: "the people shall not be his, who is about to deny him"; hence it is the people of the Lord through faith; 1 Peter 2:9: "you are a chosen race, a royal priesthood, a holy nation, a people of acquisition." "From their sins." In the book of Judges it is frequently said that such and such a one saved Israel: but from whom? From carnal enemies; but here, from sins, by remitting sins, which belongs to God alone. Luke 5:24: "but that you may know that the Son of Man has power on earth to forgive sins." Note that here Nestorius is confounded, who said that those things which belong to God, such as being from eternity, being omnipotent, or the like, do not belong to that man. Behold, that same man, who was born of the Virgin, who is called Jesus, he himself shall make his people safe from their sins. Hence, since no one can forgive sins except God alone, it must be said that this man is God, and that the things which belong to God most truly belong to him. The Evangelist had said beforehand that the mother of God was found to have in her womb one conceived of the Holy Spirit, and this he proved above through angelic revelation; here he proves it through the foretelling of prophecy; hence he says: "all this was done that it might be fulfilled which was spoken by the Lord through the prophet." And it must be known that this clause can be introduced here in two ways. Chrysostom holds that the Angel said all this and introduced the prophecy. And the reason is that he, lest what he was foretelling should seem new, wished to show at once that it had been foretold of old; Isaiah 48:3: "who has already made what is to come," according to another translation. Others say, and I believe it is better, that this, namely "all this was done," etc., are the words of the Evangelist. For there the words of the Angel end: "and he himself shall make [his people] safe," and so on. And the Evangelist introduces them for three reasons. First, that he might show that the Old Testament is about Christ; Acts 10:43: "to him all the prophets give testimony, that all who believe in him receive remission of sins through his name." Second, that they might more easily believe Christ: John 5:46: "if you believed Moses, you would perhaps believe me also: for he wrote of me." Third, to show the conformity of the Old and New Testament; Colossians 2:17: "which are a shadow of things to come, but the body is Christ's." But so that it may be known what is contained in this prophecy, it must be known that the Angel announces three things. First he said "that which is born in her," etc.; second, "she shall bring forth a son"; third, "his name shall be called Jesus." These are contained in order in the prophecy. And the first he proves by what is said, "behold the virgin"; second, by "and she shall bring forth"; third, by "and shall be called." Therefore it was of the Holy Spirit that she conceived through virginity. And this is what is said in the prophecy, "behold a virgin shall conceive"; Isaiah 35:2: "budding it shall bud forth, and shall rejoice with joy, and praising," and so on. Likewise the virgin shall bring forth a son, because in bringing forth her virginity was in no way harmed; Isaiah 11:1: "a rod shall come forth from the root of Jesse, and a flower shall rise from its root," and so on. Christ indeed is the flower. Therefore her virginity was in no way harmed. There follows: "and his name shall be called Emmanuel." But it is asked, why does this not agree with the words of the Angel, who says "and he shall be called Jesus"? It must be said that this promise was made to the Jews, who from the coming of Christ would have salvation. And "Jesus" is interpreted "savior," which is the same as Emmanuel, "God with us." For God is with us in four ways: through the assumption of nature, John 1:14: "the Word was made flesh"; through conformity of nature, since he is like in all things, Philippians 2:7: "made in the likeness of men, and found in habit as a man"; through bodily conversation, Baruch 3:38: "afterward he was seen upon the earth, and conversed with men"; through spiritual conversation, below, at the end, [Matthew] 28:20: "behold I am with you all days, even to the consummation of the world." But it must be asked, concerning the letter, why the Evangelist does not use the same words as the prophet, but uses the name Jesus. It must be said that he spoke by the same Spirit. Yet Jerome says that the Evangelist therefore said "would have," because he was already speaking of the fact as accomplished. Likewise it must be asked, why in Isaiah it is said "and he shall be called," but here it is said "and they shall call." Jerome says that here it is said "they shall call," because what the Angels first called by announcing, Luke 2:21, afterward the apostles called by preaching and magnifying; "that in the name of Jesus every knee should bow," etc., Philippians 2:10. "Which is interpreted, God with us." But it is asked, who appended this interpretation to the prophecy, "God with us" — the prophet, or the Evangelist? And it seems that it was not the Evangelist, because he did not need this, since he wrote in Hebrew. But it must be said, in one way, that because Emmanuel is a composite name, therefore the Evangelist interpreted it even though writing in Hebrew. Or it must be said that he who first translated from the Hebrew provided the interpretation. And it must be noted that in the Gloss it is said that there is a threefold species of prophecy, namely of predestination, of foreknowledge, and of threat; and they differ. For prophecy is called the foretelling of those things which are far off, that is, of future things; but of future things, some are such that God alone does them; some indeed, although God does them, nevertheless come about through us and through other creatures as well; and some are such that God does them in no way at all, as evils. The foretelling of those things which God alone does is called the prophecy of predestination, as the conceiving of the virgin; hence that saying, Isaiah 7:14: "behold a virgin shall conceive," is a prophecy of predestination. But those things which come about from secondary causes can be considered in two ways. First, according as they are in the foreknowledge of God — for example concerning Lazarus; for if someone were to consider the natural causes, he would say that he would never rise, and he would speak truly: although nevertheless he was to be raised according to the order of divine foreknowledge. Therefore when prophecy is a foretelling according as it is in the divine foreknowledge, it is always fulfilled; but when according to the order of lower causes, not always, as is clear in Isaiah 38:1, when Isaiah said to Hezekiah: "set your house in order, for you shall die, and not live," and so on. But does prophecy impose necessity on foreknowledge? And it must be said that it does not; because prophecy is a certain sign of divine foreknowledge, which does not impose necessity on the things foreknown, because it considers future things in their presentness. For whatever is done is present to God, because his gaze extends to every time; for if I see something present, my gaze does not impose necessity, just as when I see someone sitting. And in this way we have understood these prophecies which are introduced in this book. For it must be considered that there have been three errors. One is that of the Manichees, who say that in the whole Old Testament no prophecy about Christ is found: and whatever is brought in from the Old into the New Testament is entirely due to corruption. Against which, Romans 1:1: "Paul, a servant of Christ, called an apostle, set apart unto the Gospel of God, which he had promised before through his prophets," and so on. And that he speaks of the prophecies of the Jews is clear below, at chapter 9:5 [Romans 9:5]: "whose are the fathers, of whom is Christ according to the flesh," and so on. The other was that of Theodore, who said that none of the things which are brought in from the Old Testament are, according to the letter, about Christ, but are adapted, just as when they bring in that line of Virgil, "such things he recalled hanging, and remained fixed" — for this is adapted to Christ; and then that phrase "that it might be fulfilled" ought to be expounded thus, as if the Evangelist were saying: "and this can be adapted." Against which, Luke, the last chapter, 44 [Luke 24:44]: "all things must be fulfilled which are written in the law of Moses, and the prophets, and the Psalms concerning me." And it must be known that in the Old Testament there are some things which are referred to Christ, and are said of him alone, as that saying, "behold a virgin shall conceive in the womb, and bring forth a son," Isaiah 7:14; and that saying, Psalm 21:2 [Psalm 22:2]: "God, my God, look upon me, why have you forsaken me?" and so on. And if anyone were to posit another literal sense, he would be a heretic, and the heresy has been condemned. But because not only the words of the Old Testament, but also the deeds signify concerning Christ, sometimes certain things are said according to the letter about certain others, but are referred to Christ, insofar as those others bear the figure of Christ, as it is said of Solomon: "and he shall have dominion from sea to sea," etc.; for this was not fulfilled in him. The third error was that of the Jews. It must be known, however, that the Jews especially object against this authority, because in the Hebrew it does not have "virgin," but "alma," which is the same as "young girl." Hence, according to the letter, these things are not said of Christ but of Emmanuel, or, according to others, of a certain son of Isaiah. But Jerome objects against these; and that it could not have been said of the son of Isaiah is proved, because he was already born when this was said. Likewise, no one is found to have been famous at that time who was called Emmanuel. Likewise, it is not a sign that a young woman should give birth. Hence Jerome says that "alma" is an equivocal word, and signifies sometimes age, sometimes "hidden," and then it signifies a virgin diligently kept; and thus it signifies here. Likewise the Jews object that this was given as a sign. Isaiah 7:3: "two kings shall come against Achaz," etc., and he promised that they would be freed from these by giving this sign to Achaz. But it must be said that he gave this sign not only to Achaz, but also to the house of David, because he says, "hear then, O house of David"; as if the prophet were saying: the Lord will help you against this king, because he himself will do much greater things, since there will be liberation not only of him, but of the whole world. But let us return to the letter. "All this was done." But against this: the Angel had said many things beforehand, namely that "that which is born in her," etc., "she shall bring forth," etc., and again, "he shall be called," and so on. But this had not all yet been done. But it must be said, in one way, according to Rabanus, that "all this was done," etc., is referred to past deeds — that the Angel appeared to the Virgin, and spoke those words — and "all this was done" for the preserving of the Virgin, so that the word "that" is taken causally. Or it is referred to the things which he had foretold; and it can be called "wholly done" on account of predestination. Or it must be said that the Evangelist was writing when it had all already been done; and therefore it refers to that. Hence the word "that" is taken consecutively, because God did not will to become incarnate for this reason, that the prophecy might be fulfilled, as though the Old Testament were more worthy than the New; but this, that Christ should become incarnate, followed upon the prophecy.”

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“But while he thought on these things,.... While he was revolving them in his mind, considering what was most fit and proper to be done, whether to dismiss her publicly or privately; while he was consulting within himself the glory of God, the peace of his own conscience, and the credit of Mary, behold the Angel of the Lord appeared to him in a dream; probably the same Angel which appeared to Zacharias, and brought him tidings that his wife should have a son, and who also appeared to Mary, and acquainted her that she should conceive, and bring forth the Messiah, Whose name was Gabriel, Luk 1:11. If we will believe the Jews, this Angel must be Gabriel, since he is the Angel who they say (d) "is appointed over dreams"; for he appeared to Joseph in a dream, which is one of the ways and methods in which the Lord, or an Angel of his, has appeared to the saints formerly, and has answered them, see Gen 31:11 and is reckoned by the Jews (e) one of the degrees or kinds of prophecy: and so the Angel here not only encourages Joseph to take to him his wife, saying Joseph, thou son of David; which is said partly to attest his being of the house and lineage of David, and partly to raise his expectations and confirm his faith, that his wife should bring forth the promised son of David; and chiefly to engage his attention to what he was about to say, fear not to take unto thee Mary thy wife; do not be afraid either that thou shalt offend the Lord, or bring any reproach or scandal upon thyself as if thou didst connive at an adulteress; but as she is thine espoused wife, solemnly betrothed to thee, take her home to thyself, live with her as thy wife, and openly avow her as such. To which he is encouraged by the following reason or argument, for that which is conceived in her is of the Holy Ghost; she has not been guilty of any criminal conversation with men; this conception of her's is of the Holy Ghost, and entirely owing to his coming upon her, and overshadowing her in a wonderful and miraculous manner. I say, the Angel not only encourages Joseph after this manner, but delivers something to him by way of prophecy, in the following verse. (d) Zohar in Gen. fol. 103. 3. (e) Zohar in Gen. fol. 103. 3. & Maimon. Yesode Hattorah. c. 7. l. 13.”
Source
1849
A.D.
1774–1849
“Fear not to take, &c. i.e., fear not to marry her, if we suppose them not yet married, or if married already, the sense is, fear not to keep and remain with thy chaste wife; lay aside all thoughts of dismissing and leaving her. (Witham) — As the incarnation of the Son of God was effected by the whole blessed Trinity, it may be asked why this operation is peculiarly attributed to the Holy Ghost, not only here, but in Luke ii. and in the apostles’ creed? The answer is, because as power is attributed to the Father, wisdom to the Son, so goodness is attributed to the Holy Ghost, and the gifts of grace which proceed from it. (Estius in diff. loca.)”
Source
1871
A.D.
1871
“But while he thought on these things--Who would not feel for him after receiving such intelligence, and before receiving any light from above? As he brooded over the matter alone, in the stillness of the night, his domestic prospects darkened and his happiness blasted for life, his mind slowly making itself up to the painful step, yet planning how to do it in the way least offensive--at the last extremity the Lord Himself interposes. behold, the angel of the Lord appeared to him in a dream, saying, Joseph thou son of David--This style of address was doubtless advisedly chosen to remind him of what all the families of David's line so early coveted, and thus it would prepare him for the marvellous announcement which was to follow. fear not to take unto thee Mary thy wife, for that which is conceived in her is of the Holy Ghost--Though a dark cloud now overhangs this relationship, it is unsullied still.”
Source

Undated

date unknown
date
unknown
Glossa Ordinaria Medieval
“(ap. Ans.) In this is to be noted the wise soul that desires to undertake nothing rashly.”
date
unknown
“(Serm. in App. 195.) Yet though Joseph think on these things, let not Mary the daughter of David be troubled; as the word of the Prophet brought pardon to David, so the Angel of the Saviour delivers Mary. Behold, again appears Gabriel the bridesman of this Virgin; as it follows, Behold the Angel of the Lord appeared to Joseph.”
Source
date
unknown
Glossa Ordinaria Medieval
“(part Int. part Anselm.) The Angel appearing calls him by name, and adds his descent, in order to banish fear, Joseph, son of David; Joseph, as though he were known to him by name and his familiar friend.”
date
unknown
“By addressing him as son of David, he sought to recal to his memory the promise of God to David, that of his seed should Christ be born.”
“Also by the words, Fear not, he desired to shew that he knew the heart; that by this he might have the more faith in those good things to come, which he was about to speak concerning Christ.”
“There were three reasons why the Angel appeared to Joseph with this message. First, that a just man might not be led into an unjust action, with just intentions. Secondly, for the honour of the mother herself, for had she been put away, she could not have been free from evil suspicion among the unbelievers. Thirdly, that Joseph, understanding the holy conception, might keep himself from her with more care than before He did not appear to Joseph before the conception, that he should not think those things that Zacharias thought, nor suffer what he suffered in falling into the sin of unbelief concerning the conception of his wife in her old age. For it was yet more incredible that a virgin should conceive, than that a woman past the age should conceive.”
Source
date
unknown
Glossa Ordinaria Medieval
“(ord.) To be born in her, and born of her, are two different things; to be born of her is to come into the world; to be born in her, is the same as to be conceived. Or the word born is used according to the foreknowledge of the Angel which he has of God, to whom the future is as the past.”
date
unknown
“(Hil. Quæst. N. et V. Test. qu. 52.) But if Christ was born by the agency of the Holy Ghost, how is that said, Wisdom hath built herself an house? (Prov. 9:1.) That house may be taken in two meanings. First, the house of Christ is the Church, which He built with His own blood; and secondly, His body may be called His house, as it is called His temple. But the work of the Holy Spirit, is also the work of the Son of God, because of the unity of their nature and their will; for whether it be the Father, or the Son, or the Holy Spirit, that doeth it, it is the Trinity that works, and what the Three do, is of One God.”
Source
Modern · 1953 →

The in-app commentary runs from the Fathers to the early-modern record, then stops — that's where the public-domain sources end, not where the reading does. For the modern reading, follow the sources directly.