The interpretation timeline
John 6:51 Douay-Rheims

I am the living bread which came down from heaven. If any man eat of this bread, he shall live for ever; and the bread that I will give, is my flesh, for the life of the world.

A.D. 391 – 1871 9 witnesses 12 excerpts

Patristic

before A.D. 750
391
A.D.
John Chrysostom Patristic
A.D. 347–407
“In order then that we may become this not by love only, but in very deed, let us be blended into that flesh. This is effected by the food which He hath freely given us, desiring to show the love which He hath for us. On this account He hath mixed up Himself with us; He hath kneaded up His body with ours, that we might be a certain One Thing, like a body joined to a head.”
Source
416
A.D.
Augustine of Hippo Patristic
A.D. 354–430
“Believers know the body of Christ, if they neglect not to be the body of Christ. Let them become the body of Christ, if they wish to live by the Spirit of Christ. None lives by the Spirit of Christ but the body of Christ.”
“(Gloss. Nic.) Our Lord pronounces Himself to be bread, not only in respect of that Divinity, which feeds all things, but also in respect of that human nature, which was assumed by the Word of God: And the bread, He says, that I will give is My flesh, which I will give for the life of the world.”
“(Tr. xxvi. 13) But when does flesh receive the bread which He calls His flesh? The faithful know and receive the Body of Christ, if they labour to be the body of Christ. And they become the body of Christ, if they study to live by the Spirit of Christ: for that which lives by the Spirit of Christ, is the body of Christ. This bread the Apostle sets forth, where he says, We being many are one body. (1 Cor. 12:12) O sacrament of mercy, O sign of unity, O bond of love! Whoso wishes to live, let him draw nigh, believe, be incorporated, that he may be quickened.”
Source
735
A.D.
Bede the Venerable Patristic
c. A.D. 672–735
“This bread our Lord then gave, when He delivered to His disciple the mystery of His Body and Blood, and offered Himself to God the Father on the altar of the cross. For the life of the world, i. e. not for the elements, but for mankind, who are called the world.”

Medieval

c. 750 – 1100
804
A.D.
Alcuin of York Medieval
c. A.D. 735–804
“Therefore I say, He that eateth this bread, dieth not: I am the living bread which came down from heaven.”
“But men must be quickened by my life: If any man eat of this bread, he shall live, not only now by faith and righteousness, but for ever.”

Scholastic

c. 1100 – 1500
1107
A.D.
c. 1055–1107
“Which I shall give: this shews His power; for it shews that He was not crucified as a servant, in subjection to the Father, but of his own accord; for though He is said to have been given up by the Father, yet He delivered Himself up also. And observe, the bread which is taken by us in the mysteries, is not only the sign of Christ’s flesh, but is itself the very flesh of Christ; for He does not say, The bread which I will give, is the sign of My flesh, but, is My flesh. The bread is by a mystical benediction conveyed in unutterable words, and by the indwelling of the Holy Ghost, transmuted into the flesh of Christ. But why see we not the flesh? Because, if the flesh were seen, it would revolt us to such a degree, that we should be unable to partake of it. And therefore in condescension to our infirmity, the mystical food is given to us under an appearance suitable to our minds. He gave His flesh for the life of the world, in that, by dying, He destroyed death. By the life of the world too, I understand the resurrection; our Lord’s death having brought about the resurrection of the whole human race. It may mean too the sanctified, beatified, spiritual life; for though all have not attained to this life, yet our Lord gave Himself for the world, and, as far as lies in Him, the whole world is sanctified.”
Source
1270
A.D.
Thomas Aquinas Catholic
1225–1274
“With the murmuring of the Jews checked, the Lord accordingly satisfies the doubt that had arisen in the hearts of the Jews concerning the word he had spoken, namely, I am the bread which came down from heaven, where he intends to prove that this is true of himself; and he argues thus: that bread came down from heaven which gives life to the world; but I am the bread giving life to the world; therefore I am the bread which came down from heaven, and so on. Concerning this he does three things. First, he sets down, as it were, the minor premise of his argument, namely, I am the bread of life; second, he sets down the major premise, namely, that the bread which came down from heaven ought to give life, at the place, your fathers ate manna in the desert, and they died; third, he sets down the conclusion, at the place, I am the living bread. Concerning the first he does two things. First he makes clear his proposal; second he brings forward what was intended as, so to speak, proven, at the place, I am the bread of life. His proposal is to show that he is the bread of life. Now bread gives life inasmuch as it is taken. But it is agreed that whoever believes in Christ takes him within himself, according to that word of Ephesians 3:17: that Christ may dwell through faith in our hearts. If therefore he who believes in Christ has life, it is clear that by eating this bread he is given life; therefore this bread is the bread of life. And this is what he says: Amen, amen, I say to you, whoever believes in me — namely with formed faith, which perfects not only the intellect but also the affection (for one does not tend toward the thing believed unless one loves it) — has eternal life. Now Christ is in us in two ways: namely in the intellect through faith, inasmuch as it is faith; and in the affection through charity, which informs faith: 1 John 4:16, whoever abides in charity abides in God, and God in him. Whoever therefore believes in Christ in such a way as to tend toward him has him in affection and in intellect; and if we add that Christ is eternal life, as is said in 1 John 5:20, that we may be in his true Son Jesus Christ: this is the true God and eternal life; and above, John 1:4, in him was life — we can infer that whoever believes in Christ has eternal life. He has it, I say, in cause and in hope, and will one day have it in reality. Having made clear his proposal, he brings forward what was intended, when he says, I am the bread of life, that is, giving life, as evidently follows from what has been said. Concerning this bread, Genesis 49:20: Asher, his bread is fat, he shall yield delights — namely of eternal life — to kings. Accordingly, when he says, your fathers ate manna in the desert, and they died, he sets down the major premise: namely, that to give life is the effect of bread descending from heaven. And first he prefaces the manifestation of the proposal; second he sets down what was intended, at the place, this is the bread which comes down from heaven. Now he makes clear his proposal by its contrary. For it was said above that Moses did not give the Jews bread from heaven, but only from the air; but all bread which is not from the true heaven cannot give sufficient life; therefore this is proper to heavenly bread, that it gives life. And therefore the bread of Moses, in which you take pride, does not give life; and this he proves when he says, your fathers ate manna in the desert, and they died. Here he first reproaches their vice, when he says your fathers, etc. — whose sons you are, not only according to the origin of the flesh, but also according to the imitation of their works, because you are murmurers, just as they also murmured in their tents, as is said in Psalm 105:25; and therefore he said to them, Matthew 23:32, fill up the measure of your fathers. Whence, as Augustine says, the people are said to have offended God in no matter more than by murmuring against God. Second, he insinuates the short span of time, when he says in the desert: for it was not a long time in which the manna was given to them, nor did it come with them into the land of promise, but only in the desert, as is said in Joshua 5:12. This bread, however, preserves and refreshes forever. Third, he makes clear the deficiency of the food, because it did not preserve unfailing life; hence he says, and they died. For, as is found in Joshua 5, all who murmured, except Joshua and Caleb, died in the desert. Whence this was also the cause of the second circumcision, namely that all the people who went out from Egypt died in the desert, as is said in the same place. But it is asked of what death God here speaks. For if he speaks of bodily death, there will be no difference between that bread which was in the desert and our bread which came down from heaven, because even Christians who take this one die bodily. But if he speaks of spiritual death, it is clear that here and there some die spiritually and some do not. For Moses, and many who pleased God, did not die, although others died. Likewise, those who take this bread unworthily also die spiritually; 1 Corinthians 11:29: for he who eats and drinks unworthily eats and drinks judgment to himself. To this it must be said that that food agrees with our spiritual food. They agree indeed as to this, that each signifies the same thing: for both that one and this one signify Christ, on account of which it is called the same food; 1 Corinthians 10:3: all ate the same food. He says the same because both are a figure of spiritual food. But they differ, because that one only prefigured, whereas this bread contains what it prefigures, namely Christ himself. It must therefore be said that each of these foods can be taken in two ways: either as to the sign only, that is, that it is taken only as food, its meaning not understood; and by this neither spiritual nor bodily death is removed. Or it can be taken as to both, that is, that the visible food is so taken that the spiritual food is understood, and is spiritually tasted, so that it spiritually satisfies; and in this way those who ate the manna spiritually did not die spiritually. But those also who eat the Eucharist spiritually, and now live spiritually without sin, will also live bodily forever. Our food, therefore, has more than their food, because it contains in itself what it prefigures. Having made clear the proposal, therefore, he brings forward what was intended; hence he says, this is the bread which comes down from heaven. And according to the Gloss, he says this pointing to himself. But this is not the Lord's meaning, because since he immediately adds, I am the living bread which came down from heaven, it would be a repetition of words. It must therefore be said that the Lord intends this: namely, to say that that bread comes down from heaven which can do this, namely give life; but I am such; therefore I am the bread which comes down from heaven. And the reason that bread coming down from heaven gives unfailing life is that all food nourishes according to the property of its own nature; but heavenly things are incorruptible; and therefore, because that food is heavenly, it is not corrupted, and as long as it remains it gives life. Whoever therefore eats of it will not die. Just as if some bodily food were never corrupted, giving nourishment, it would always give life. And therefore this bread was signified by the tree of life which was in the middle of paradise, in a certain way giving life forever, according to that word of Genesis 3:22: now therefore lest perhaps he put forth his hand, and take of the tree of life, and eat, and live forever. If therefore this is the effect of this bread, namely that whoever eats of it does not die, and I am such: therefore, and so on. I am the living bread, etc. Concerning this, then, he does two things. First he speaks of himself in general; second specifically, at the place, and the bread which I will give is my flesh. Concerning the first he does two things. First he concludes the origin of himself. Second he shows his power, at the place, if anyone eats of this bread, he will live forever. He said, then, I am the living bread, and therefore I can give life. For bodily bread does not give life forever, because it does not have life in itself; but it gives life, once altered and converted into nourishment, by the power of the one living. Who came down from heaven: this was expounded above, in chapter 3, namely how he came down. And by this the heresies of those saying Christ was a mere man are excluded, because according to this he would not have come down from heaven. Now his power is to give eternal life; and therefore he says, if anyone eats of this bread — spiritually, that is — he will live, not only in the present through faith and righteousness, but forever; below, John 11:26: everyone who lives and believes in me will never die. Accordingly he speaks of the body, when he says, and the bread which I will give is my flesh. For he had said that he was the living bread, and lest it be understood that this belonged to him only inasmuch as he is the Word, or according to the soul only, he therefore shows that his flesh also is life-giving: for it is the instrument of his divinity; hence, since an instrument acts by the power of the agent, just as the divinity of Christ is life-giving, so also, as Damascene says, the flesh, by the power of the Word joined to it, gives life; hence Christ by his touch healed the sick. Thus, then, what he said above, I am the living bread, pertains to the power of the Word; but what he adds here pertains to the communion of his body, namely to the sacrament of the Eucharist. Here we can consider four things concerning this sacrament: namely, its species, the authority of its institutor, the truth of the sacrament, and its usefulness. The species of the sacrament indeed: this is bread; Proverbs 9:5: come, and eat my bread. The reason for this is that this is the sacrament of the body of Christ; but the body of Christ is the Church, which rises into the unity of one body out of many faithful; hence this is the sacrament of the unity of the Church; Romans 12:5: we are all one body. Because, then, bread is made up of many grains, therefore this species is fitting for this sacrament; and therefore he says, and the bread which I will give is my flesh. The author of this sacrament is Christ: for although the priest consecrates, nevertheless Christ himself gives power to the sacrament, because even the priest himself consecrates in the person of Christ. Hence in the other sacraments the priest uses his own words, or those of the Church, but in this one he uses the words of Christ: because just as Christ gave his own body to death by his own will, so by his own power he gives himself as food; Matthew 26:26: taking bread, he blessed, and broke it, and gave it to his disciples, and said, take and eat: this is my body. And therefore he says, which I will give: and he says I will give, because this sacrament was not yet instituted. Now the truth of this sacrament is insinuated when he says, is my flesh. He does not say, however, signifies my flesh, but is my flesh; because according to the truth of the matter, what is taken is truly the body of Christ; Job 31:31: if the men of my tabernacle have not said: who will give us of his flesh, that we may be filled? But since in this sacrament the whole Christ is contained, why did he say only, is my flesh? In answer to this, it must be known that in that mystical sacrament the whole Christ is contained according to truth, but the body is there by force of the conversion, while the divinity and the soul are there by natural concomitance. For if it be granted — though impossible — that the divinity were separated from the body of Christ, the divinity would no longer be in the sacrament. Likewise also, if someone had consecrated during the three days of his death, the soul of Christ would not have been there, but such a body as it was on the cross, or in the tomb. The reason he rather says flesh is that, since this sacrament is a remembrance of the Lord's passion, according to that word of 1 Corinthians 11:26: as often as you shall eat this bread, and drink the cup, you shall show forth the death of the Lord — and the passion of Christ was from weakness, according to that word of 2 Corinthians 13:4: he died from weakness, etc. — therefore, so that the weakness from which he died might be insinuated, he rather says, is my flesh: for this word signifies weakness. Now the usefulness of this sacrament is great, and universal. Great indeed, because it works in us now spiritual life, and at length eternal life, as has been said. For, as appears from what has been said above, since this sacrament is of the Lord's passion, it contains in itself Christ having suffered; hence whatever is the effect of the Lord's passion is also wholly the effect of this sacrament. For this sacrament is nothing other than the application of the Lord's passion to us. For it was not fitting that Christ should always be with us according to his presence; and therefore he willed to supply for this through this sacrament. Whence it is clear that the destruction of death, which Christ destroyed by dying, and the reparation of life, which he effected by rising, is the effect of this sacrament. Universal, however, because the life which it confers is not only the life of one man, but, as far as it is in itself, of the whole world: for which the death of Christ is sufficient; 1 John 2:2: he is the propitiation for our sins, and not for ours only, but also for those of the whole world. It must be noted, however, that it is one way in this sacrament, and another way in the others: for the other sacraments have singular effects, as in Baptism only the one baptized receives grace; but in the immolation of this sacrament the effect is universal, because not only does the priest obtain the effect, but also those for whom he prays, and the whole Church, both of the living and of the dead. The reason for this is that in it is contained the universal cause itself of all the sacraments, namely Christ. Nor yet, if a layman takes this sacrament, does it profit others as far as concerns the work performed, inasmuch as it is considered as reception; although from the intention of the one performing it and of the one receiving it, it can be communicated to all to whom he directs his intention. From which it is clear that laypeople who receive the Eucharist for those who are in Purgatory are in error.”

Post-Reformation

c. 1650 – 1900
1832
A.D.
Adam Clarke Methodist
1762–1832
“Is my flesh, which I will give, etc. - Our Lord explains his meaning more fully, in these words, than he had done before. Having spoken so much of the bread which feeds and nourishes the soul, and preserves from death, the attention of his hearers was fixed upon his words, which to them appeared inexplicable; and they desired to know what their meaning was. He then told them that the bread meant his flesh, (his life), which he was about to give up; to save the life of the world. Here our Lord plainly declares that his death was to be a vicarious sacrifice and atonement for the sin of the world; and that, as no human life could be preserved unless there was bread (proper nourishment) received, so no soul could be saved but by the merit of his death. Reader, remember this: it is one of the weightiest, and one of the truest and most important sayings in the book of God.”
Source
1849
A.D.
1774–1849
“Christ now no longer calls the belief in him, or the preaching of the gospel, the bread that he will give them; but he declares that it is his own flesh, and that flesh which shall be given for the life of the world. (Calmet) — This bread Christ then gave, when he gave the mystery of his body and blood to his disciples. (Ven. Bede)”
Source
1871
A.D.
1871
“I am, &c.--Understand, it is of MYSELF I now speak as the Bread from heaven; of MEif a man eat he shall live for ever; and "THE BREAD WHICH I WILL GIVE IS MY FLESH, WHICH I WILL GIVE FOR THE LIFE OF THE WORLD." Here, for the first time in this high discourse, our Lord explicitly introduces His sacrificial death--for only rationalists can doubt this not only as that which constitutes Him the Bread of life to men, but as THAT very element IN HIM WHICH POSSESSES THE LIFE-GIVING VIRTUE.--"From this time we hear no more (in this discourse) of "Bread"; this figure is dropped, and the reality takes its place" [STIER]. The words "I will give" may be compared with the words of institution at the Supper, "This is My body which is given for you" (Luk 22:19), or in Paul's report of it, "broken for you" (Co1 11:24).”
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.