The interpretation timeline
Matthew 6:6 Douay-Rheims

But thou when thou shalt pray, enter into thy chamber, and having shut the door, pray to thy Father in secret: and thy Father who seeth in secret will repay thee.

1256 – 1871 4 witnesses

Scholastic

c. 1100 – 1500
1256
A.D.
Thomas Aquinas Catholic
1225–1274
“Peter of Scala, On Matthew, chapter 6, lecture 2: "And when you pray, you shall not be as the hypocrites." Here he removes, in the second place, the desire for human favor from prayer, and this contains three parts. First he excludes the desire for human favor; second he teaches the manner of praying, at "But thou, when thou shalt pray"; third he subjoins the due form of prayer, at "Thus therefore shall you pray," etc. The first part contains three things. First he removes from prayer the ostentation of hypocrites; second, the manner and end of that ostentation, at "who love to stand and pray in the synagogues and corners of the streets"; third he subjoins their condemnation, at "Amen I say to you, they have received their reward." He says therefore "and when you pray," that is, out of the affection of the mind. But here there is a question of the letter: why did he not say, in the singular, "when thou prayest," as he did above, and "when thou doest," etc.? Response: he speaks in the plural, "when you pray," because prayer belongs to all, since nothing temporal is required for it, only the intention of the heart; but giving alms does not belong to all. Or it may be said that prayer is made in two ways: in common, as in choir, and in solitude, etc. "You shall not be as the hypocrites," shining outwardly, foul within, below, chapter 23:27. "Who love." But it is asked why he does not say, "who pray." Chrysostom's response: because in truth they do not pray, but love to be seen as though they were praying. Along the same line it is asked why he did not say the same thing about almsgiving. Response: because although they give alms with an evil intention, they nevertheless give the thing itself. "In the synagogues," where the learned gather to pray, so that they may be seen. "Standing." He says this because it is the custom of the Jews to pray standing, since they received the law standing; Exodus 19:17, "they stood at the foot of the mountain," etc. "And in the corners of the streets," supply: they love to pray. Chrysostom: they seek to hide themselves so that they may be praised in a twofold way: first, because they pray; second, because they pray secretly. "That they may be seen by men." Behold the empty intention. Chrysostom: they do not intend to be heard, but to be seen; likewise the same: O madness of vanity! They do not wish to be what they desire to appear: they pray falsely, since they do not pray; and they are falsely praised, since they are not praiseworthy. They sell an empty semblance of religion, and they buy an empty word of praise. When the word is finished, the good that was placed in the word is also finished. Whence he fittingly subjoins, "Amen I say to you," as if to say: know for certain that "they have received their reward"; the Gloss: human praise; but from me they will receive eternal punishment. "But thou, when thou shalt pray," etc. This is the second part, where he gives the manner of praying. And first he shows the due manner; second he excludes from that manner the rite of the pagans, that is, much speaking, at "And when you are praying, speak not much." The first part is divided into two: first he gives the manner of praying; second he subjoins the promise, at "and thy Father, who seeth in secret, will repay thee." Now the manner of praying consists in three things. First, in the secrecy of meditation; second, in the exclusion of depraved affection, at "and having shut the door"; third, in rectitude of intention, at "pray to thy Father in secret." He says therefore, "but thou, when thou shalt pray, enter into thy chamber," that is, into the secrecy and inner recess of the mind, as Augustine says, and Rabanus, by the act of secret meditation. Chrysostom: God is not to be moved by a clamorous voice, but is to be appeased by a right conscience, for he is a hearer not of the voice but of the heart. Or, "enter into thy chamber" according to the letter. And he pointedly says "chamber," because then the soul ought to rest from external things when it prays; and then is the more fitting time, and the place more secret. Chrysostom: through the day a thousand causes surround you and do not permit you to be secret for prayer. But when you come to your bed, say to your soul: soul, how have we spent the day? What good or evil have we done? Ask God first, and then permit your soul to fall asleep. Thus did Judith, Judith 8:6; thus Peter, Acts 10:9; and Tobias, Tobit 3:10. "And having shut the door," that is, with every depraved and worldly affection excluded, or with the outer senses closed, as the Gloss says. Isaiah 26:20: "Go, my people, into thy chambers, and shut thy doors upon thee." "Pray to thy Father," the Gloss: he who is prayed to in spirit and in truth, John 4:23. Pray, not concerning worldly things. Isidore: far from God is the soul that has been occupied with the thoughts of the age. Jerome: it is one thing to relate to one who does not know, another to ask one who knows: the former is a disclosure, the latter a service. "In secret," that is, in the innermost part of the heart. Chrysostom: let the one praying do nothing new for men to look at, nor cry out with the voice, nor spread out the hands, nor shamelessly lift the eyes to heaven, so as to become conspicuous. "And thy Father, who seeth in secret, will repay thee." Behold, he subjoins the promise, saying, "and thy Father, who seeth in secret," that is, who beholds the heart; Hebrews 4:13: "all things are naked and open to his eyes." "Will repay thee." He does not say "will give," because he has already constituted himself a debtor, that is, he will for certain repay you the reward. Chrysostom: consider the philanthropy of God, that is, the love which he has for men; and consider with wonder the mercy of God, since even for those goods which are asked of him he promises to give a reward. "And when you are praying, speak not much." Here he excludes much speaking from prayer, where first he sets down the prohibition of much speaking; second the reason for the prohibition, at "Be you not therefore like to them." He says therefore, "and when you are praying, speak not much," that is, do not put your trust in words. On the contrary: 1 Thessalonians, last chapter, 17: "Pray without ceasing." Moreover the Lord persevered long in prayer, below, chapter 26:36ff., and Luke 6:12. The response, according to Augustine: he condemns much speaking arising from unbelief, but not the prayers which the saints make in purity of heart. Whence Anselm: it is not a sin to pray with devotion of heart through many words. "As the heathens do," for the gentiles multiplied words in their prayers, first, so that they might indicate their intention to the demons whom they worshiped, since otherwise the demons could not have known it; whence Augustine: for the gentiles a multiplicity of words was necessary on account of the demons. Second, so that they might call back to themselves the demons who were absent; and to this cause Elijah alludes, 1 Kings 18:27, saying to the priests of Baal, when they had prayed for a long time: "Cry with a louder voice: for he is a god, and perhaps he is talking, or is in an inn, or on a journey, or perhaps he is asleep, and must be awaked." Third, so that by the persuasion of words they might incline them to mercy; whence he adds: "for they think that in their much speaking they may be heard," that is, they suppose that by a multitude of persuasive words their prayers are made effective. And because they do so, "therefore be you not," my faithful ones, "like to them," namely in much speaking, so that you should believe God to be inclined by persuasive words. Isidore: men are not heard for their much speaking, as though they were striving by more words to bend God. Likewise, lest you think your God ignorant of what you ask: "for your Father knoweth what is need­ful for you." Behold the reason for the prohibition; as if to say: it is not fitting for you to pray with many words, but with deeds and with a simple affection of heart, says Rabanus. "For your Father knoweth what is need," that is, what is necessary for you, "before you ask him." Why then is it fitting to pray? Response: not that you may teach him, but that you may bend yourself, that you may be made familiar with him, that you may be humbled, that you may be reminded of your sins. And he pointedly says, "your Father." Chrysostom: by saying "Father," he signified in one word both the forgiveness of sins, and the destruction of punishments, and justification, and sanctification, and liberation, and the adoption of sons, and the inheritance of God, and brotherhood joined with the Only-Begotten, and the most abundant gifts of the Holy Spirit. Here Jerome and Rabanus ask: if God knows before we ask, to what purpose do we ask one who knows? Response: manifold is the reason why we speak to one who knows, and why we pray. The first, that we may profess and know that we have from him that which we ask; whence Rabanus: it is not necessary to relate, but to beseech. The second, that an example may be furnished; whence Rabanus: God wishes to be asked, so that his goodness may be conveyed to the peoples. The third, that our mind may be roused; whence Jerome: at the time of prayer we rouse ourselves. The fourth, that devotion may be roused in those standing by. Jerome: we speak, not that we may make a disclosure of our own will, but that we may rouse the service of pious devotion. The fifth, that desire may be kindled. The sixth, that the heart may be purified. Concerning these two the interlinear Gloss: by words the heart is kindled, and by prayers it is made serene. The seventh, that the mind, occupied about holy words, may be withdrawn from superfluous thoughts.”

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“But thou, when thou prayest, enter into thy closet,.... Or "chamber", a secret place, fit for private retirement, meditation, and prayer. And when thou hast shut thy door; see some such like phrases in Isa 26:20 where they are used to express security, here secrecy. Our Lord does not mean to exclude and condemn public prayer, in joining with few, or more persons, in such service; for he himself directs to it, and approves of it, Mat 18:19 but his view is to instruct persons that they should not only pray in public, but in private also; and especially the latter, which is more suitable and fitting for their particular cases, and less liable to pride, hypocrisy, and vanity. Pray to thy Father, which is in secret; who is invisible; not to be seen with the eyes of the body, but to be approached with a true heart, in faith and fear, through his Son Jesus Christ, the only mediator between God and man; and who is the image of the invisible God, and in whom he is pleased to manifest himself to his people, so as he does not unto the world: and thy Father, which seeth in secret, observes and takes notice of the secret breathings, pantings, desires, and requests of thy heart and lips, shall reward thee openly, both here and hereafter; by pouring into thy bosom all the good things thou hast been praying for, both for time and eternity. This is agreeable to what the Jews sometimes say, "that a man ought not to cause his voice to be heard in prayer; but should pray "silently", with a voice that is not heard; and this is the prayer which is daily accepted (g).'' (g) Zohar in Gen. fol. 114. 4.”
Source
1849
A.D.
1774–1849
“Because he who should pray in his chamber, and at the same time desire it to be known by men, that he might thence receive vain glory, might truly be said to pray in the street, and sound a trumpet before him: whilst he, who though he pray in public, seeks not thence any vain glory, acts the same as if he prayed in his chamber. (Menochius) — Jesus Christ went up to the temple, to attend public worship on the festival days.”
Source
1871
A.D.
1871
“But thou, when thou prayest, enter into thy closet--a place of retirement. and when thou hast shut thy door, pray to thy Father which is in secret; and thy Father which seeth in secret shall reward thee openly--Of course, it is not the simple publicity of prayer which is here condemned. It may be offered in any circumstances, however open, if not prompted by the spirit of ostentation, but dictated by the great ends of prayer itself. It is the retiring character of true prayer which is here taught. Supplementary Directions and Model Prayer (Mat 6:7-15).”
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.