The interpretation timeline
Isaiah 49:21 Douay-Rheims

And thou shalt-say in thy heart: Who hath begotten these? I was barren and brought not forth, led away, and captive: and who hath brought up these? I was destitute and alone: and these, where were they?

A.D. 397 – 1875 6 witnesses

Patristic

before A.D. 750
397
A.D.
Ambrose of Milan Patristic
A.D. 339–397
“We are to be a model for everyone around us, not just in our actions but also in our speech, in our chastity and in our faith. Let us be what we should wish others to think us, and let us show our feelings as they really are. We should never mutter a word that is unjust, even in our own heart, thinking to ourselves that it is hidden under a veil of silence; for the One who made the secret places hears words that are spoken in secret, and the One who implanted the power of thought in our innermost parts knows the hidden things that those innermost parts contain. So as people who live under the eyes of their Judge, let us remember that everything we do is exposed to the light, and in this way it will be manifest to all.”
Source

Scholastic

c. 1100 – 1500
1105
A.D.
Rashi Jewish
1040–1105
“and solitary solede in O.F. rejected Rejected by everyone. All say about me, “Turn away from her.””
1167
A.D.
Ibn Ezra Jewish
1089–1167
נלמודה Desolate. Remaining lonely; comp. גלמוד solitary (Job 3:7). It is an adjective, of a quadriliteral root. וסורה And removing to and fro. It is an adjective, and not a participle passive; for סור to depart is a neuter verb. איפה where. It is a compound of two words אי and פה
1256
A.D.
Thomas Aquinas Catholic
1225–1274
“Hear, O islands, etc. In this part he pursues the order of the liberation more specifically; and concerning this he does two things. First the people confesses the benefits received; second it receives the promise of things to come, there, I said: in vain, etc. Concerning the first, four benefits are confessed. First, the privilege of the divine election; and it continues why the prophet had above enjoined the people, that they should announce it. Whence immediately is subjoined the voice of the people announcing, and saying, Hear. From the womb, choosing me in the fathers themselves. Ps. 21: From the womb of my mother, God, etc. Second, the efficacy of prayer: and he set the mouth, prayer, as a sword, penetrating even to the ears of God and the depths of his mercy, Eph. ult.: the sword of the spirit, etc. Third, the help of divine protection: in the shadow, that is, under the protection of his power, as an archer hides a chosen arrow, to preserve it. Ps. 16: under the shadow of thy wings, etc.; Ps. 26: he hath hidden me in his tabernacle, etc. Fourth, the glory of the divine power: and he said to me: in thee will I glory; through the great things shown in thee I will appear glorious. Above, 43: every one that calleth upon my name, etc. According to others, this is the voice of Cyrus, whose name was foretold by Isaiah above, 45, before he was born; whose threatening words were as a sword, and he was protected lest his grandfather should kill him, and was kept as a chosen arrow for the appointed time; to whom it was announced that the people of Israel was the servant of God. Otherwise it is expounded of Christ; whose name was foretold by the Angel; the word of preaching, a sword piercing hearts; protected, on account of the weakness of the flesh, by the power of the divinity, and chosen among all for the fulfilling of the salvation of the human race. And he is called Israel, because he was born of the people of Israel according to the flesh. I said: here the Lord promises future benefits: and first he promises the prophet Isaiah exaltation; second, to the people liberation, there, thus saith the Lord the redeemer, etc. Concerning the first, two things. First is set down the allegation of the prophet, setting forth his labor in preaching, although through the fault of the hearers no fruit followed: and he concludes: therefore my judgment, on my behalf, is with the Lord, before him, and my work, as pleasing to him. Jer. 6: the founder hath melted in vain, etc. Second, he sets down God's response: and now thus saith the Lord: and first is signified the acceptance of the allegation, that I may bring back, as if to say: choosing me from the womb of my mother for this, that I might recall his people to him. And yet Israel shall not altogether be gathered, to him through my preaching. And yet I am glorified, etc.; Habac. 3: God, the Lord, is my strength, etc. Second, the response itself is set down, and he said: it is a small thing, as if to say: so greatly will I honor thy ministry that not only among the Jews, but among all the nations, my salvation shall be announced through thee. Rom. 3: is he the God of the Jews only? etc. This too is plainly expounded of Christ, who by his preaching and the consummation of his death made little fruit among the Jews, but enlightened and saved the nations. Likewise also of Cyrus, though more forcedly, who through his kindnesses, according to the Lord's intention, recalled the people to the worship of God, and yet did not succeed, to whom dominion over many nations was given by God. Thus saith the Lord the redeemer, etc. Here he promises liberation: and concerning this he does two things. First he promises liberation; second he excludes their doubt, there, and Sion said, etc. Concerning the first, three things. First, the things preceding liberation, namely the veneration of the Jews, which was the cause of the liberation; recalling their former contempt: contemptible, on account of the people's weakness; abominable, on account of the singularity of their worship; a servant, on account of subjection to diverse nations, above, 18: to a nation rent asunder, etc.; and he sets down the veneration itself: kings shall see the great things I will show for thee, and shall adore, as, according to the letter, Nabuchodonosor, Dan. 2, and Cyrus, and his other princes honored Esdras. Another preamble is the exaltation of the liberating king, namely Cyrus: in an acceptable time, and he does not determine the time of the exaltation: acceptable, when it shall please me to save my people, I have heard, exalting thee into a kingdom, according to thy desire, and the fruit of the exaltation: and I have preserved, etc., for the fulfilling of the covenant of my people. Be revealed, that is, be enlightened. Or of Christ, who in his passion was despised, and judged as it were a servant. Below, 53: we saw him despised, etc., but afterward, according to the letter, adored by kings. Ps. 71: all kings shall adore him, etc.; in an acceptable time, namely the time of grace. 2 Cor. 6: behold, now is the time, etc. Second, he sets down the things consequent upon the liberation, promising to the liberated an abundance of good things: they shall feed in the ways; that is, they shall enjoy consolations as abundantly as sheep enjoy pastures, when they are found even in the way, beyond the usual. Ezech. 34: they shall rest in the grass, etc.; as to the absence of evils, both of want, he shall not hunger, etc., and of harm inflicted, the heat, of tribulation; and the sun, the tyrant causing it. Ps. 120: the sun shall not burn by day, etc.; and he assigns the cause of both. Because he that is merciful, etc.; of waters, of consolations. Ps. 22: the Lord ruleth me. Third, he promises the liberation itself, setting down the preparation of the ways: and I will make all the mountains; that is, the princes will help you to return. Above, 40: every valley shall be filled, etc.; setting down also the return of the captives: behold these from afar, from the east, the sea, the west. Jer. 31: I will bring them from the north, etc.; he sets down also the giving of thanks: praise, ye heavens, etc.; Ps. 68: let the heavens praise him, etc. And Sion said, etc. Here he excludes their doubt: and first that which arose from the divine indignation; second that which arose from their dejection, there, and thou shalt say in the heart, etc.; third that which arose from the power of the enemies, there, shall it be taken away, etc. Concerning the first, two things. First he sets down the doubt: hath forsaken, without help; and therefore I cannot hope for liberation. Baruch 4: I am forsaken, etc.; second he excludes it by the likeness of a mother: is it possible, etc.; Jer. 31: if a son honorable, etc.; third he applies the promise concerning the restoration of the city: and first as to the rebuilding of the walls, setting down the divine purpose: behold, in my hands; as if to say: thus I hold thee in memory, as one who writes, or makes some sign on his hand, that he may be mindful of some thing. Thy walls; as if to say, now I see the rebuilding of thy walls. Job 37: he hideth in the hands, etc.; Ps. 89: a thousand years before the eyes, etc.; and the manner of the fulfillment: builders have come, that is, rebuilders, namely Zorobabel, and Jesus, and others, already in my eyes; the scatterers, the Chaldeans. Zach. 4: the hands of Zorobabel, etc. Second, as to the habitation of men: and concerning this he does three things. First, the gathering together of the citizens: lift up round about, etc.; Baruch 4: look about, Jerusalem, etc. Second, the re-inhabiting of the city, showing that it shall be inhabited. As I live, the manner of an oath; as with an ornament — as a bride with garments, so the city is adorned with citizens. Below, 61: he hath clothed me with the garment of salvation, etc.; showing that it shall be filled with inhabitants: for the desert places, as to inhabitants, the solitudes, as to the tillers, the ruins, as to the destroyed walls. Zach. 2: it shall be inhabited without a wall, etc.; he shows also that it shall be emptied of enemies: and far, etc. Third, he foretells the multitude of the inhabitants: still shall the children of sterility say, that is, those who were born when thou didst believe thyself barren, emptied of inhabitants. Below, 54: enlarge the place of the tent, etc. And thou shalt say in the heart, etc. Here he excludes the second doubt: and first he sets down the wonder, and thou shalt say, out of wonder: barren, because there were not in me men who could beget children; destitute, of divine help. Below, 66: who hath ever heard such, etc. Second he excludes the doubt, setting down the manner of the multitude of the inhabitants: thus saith the Lord: as to four things. First, as to the divine inspiration: behold I will lift up the hand, as it were making a sign; above, 11: he shall lift up a sign among the nations, etc. Second, as to the honorable bringing back: and they shall bring in the arms, in which is signified the help which they had from the nations. Kings, foster-fathers, providing for thee in necessities. Baruch 5: the Lord will bring them to thee, etc. Third, as to the exaltation of the liberated: with the face to the earth, this especially at the time of the Machabees; below, 40: they shall come to thee bowed down, etc. Fourth, he assigns the reason for this: and thou shalt know that I, etc.; Ps. 70: in thee, O Lord, have I hoped, let me not be confounded, etc. Shall it be taken away. Here he excludes the third doubt: and first he sets it down, from the strong, Nabuchodonosor; Matth. 12: or how can one enter, etc. Second he excludes it: for thus he saith, first setting down the benefit of the liberation: the captivity, namely of the Jews. Job 29: I broke the jaws of the wicked one, etc.; second, the manner of the liberation, setting down the destruction of the enemies. But them, namely the Chaldeans, they judged, unjustly. Soph. 3: I will kill, etc.; and he sets down the determination of the punishment: and I will feed: either on account of dissension, as above, 9: every man the flesh of the arm, etc., or on account of the multitude of the dead, while the mouth of one fell upon the blood of another, as if he would drink: or on account of famine. Third, he sets down the fruit of the liberation: and all flesh shall know, etc.; above, 40: all flesh shall see, etc.”

Post-Reformation

c. 1650 – 1900
1871
A.D.
1871
“Who, &c.--Zion's joyful wonder at the unexpected restoration of the ten tribes. Secondarily, the accession of spiritual Israelites to the mother church of Jerusalem from the Gentiles is meant. This created surprise at first (Act 10:45; Act 14:27; Act 15:3-4). lost . . . am desolate, a captive, and removing to and fro--rather, "bereaved of . . . have been barren, an exile and outcast" [HORSLEY]. She had been "put away" by Jehovah, her husband (Isa 50:1); hence her wonder at the children begotten to her.”
Source
1875
A.D.
Keil & Delitzsch Lutheran
1861–1875
“The words that sound in the ears of Zion are now followed by the thought of astonishment and surprise, that rises up in her heart. "And thou wilt say in thy heart, Who hath borne me these, seeing I was robbed of children, and barren, banished, and thrust away; and these, who hath brought them up? Behold, I was left alone; these, where were they?" She sees herself suddenly surrounded by a great multitude of children, and yet she was robbed of children, and galmūdâh (lit. hard, stony, Arab. 'galmad, 'gulmūd, e.g., es-sachr el'gulmūd, the hardest stone, mostly as a sugstantive, stone or rock, from gâlam, from which comes the Syriac gelomo, stony ground, related to châlam, whence challâmı̄sh, gravel, root gal, gam, to press together, or heap up in a lump or mass), i.e., one who seemed utterly incapacitated for bearing children any more. She therefore asks, Who hath borne me these (not, who hath begotten, and which is an absurd question)? She cannot believe that they are the children of her body, and her children's children. As a tree, whose foliage is all faded away, is called nōbheleth itself in Isa 1:30, so she calls herself gōlâh vesūrâh, extorris et remota (sūr = mūsâr, like sūg in Pro 14:14 = nâsōg or mussâg), because her children have been carried away into exile. In the second question, the thought has dawned upon her mind, that those by whom she finds herself surrounded are her own children; but as she was left alone, whilst they went forth, as she thought to die in a foreign land, she cannot comprehend where they have been hitherto concealed, or where they have grown up into so numerous a people.”
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.