50 This is the bread which cometh down from heaven, that a man may eat thereof, and not die.
[AD 407] John Chrysostom on John 6:47-51
(Hom. xlvi. s. 1) We are all from God. That which belongs peculiarly and principally to the Son, He omits the mention of, as being unsuitable to the weakness of His hearers.

([Nic.] Theoph.) The multitude being urgent for bodily food, and reminding Him of that which was given to their fathers, He tells them that the manna was only a type of that spiritual food which was now to be tasted in reality, I am that bread of life.

(Hom. xlv. 1) He calls Himself the bread of life, because He constitutes one life, both present, and to come.

(Hom. xlvi. 2) The addition, In the wilderness, is not put in without meaning, but to remind them how short a time the manna lasted; only till the entrance into the land of promise. And because the bread which Christ gave seemed inferior to the manna, in that the latter had come down from heaven, while the former was of this world, He adds, This is the bread which cometh down from heaven.

(Hom. xlvi. 2) He then gives them a strong reason for believing that they were given for higher privileges than their fathers. Their fathers eat manna and were dead; whereas of this bread He says, that a man may eat thereof, and not die. The difference of the two is evident from the difference of their ends. By bread here is meant wholesome doctrine, and faith in Him, or His body: for these are the preservatives of the soul.

[AD 430] Augustine of Hippo on John 6:47-51
(Tr. xxvi. s. 10.) Our Lord wishes to reveal what He is; Verily, verily, I say unto you, He that believeth on Me, hath everlasting life. As if He said; He that believeth on Me hath Me: but what is it to have Me? It is to have eternal life: for the Word which was in the beginning with God is life eternal, and the life was the light of men. Life underwent death, that life might kill death.

(Tr. xxvi. 11) And because they had taunted Him with the manna, He adds, Your fathers did eat manna in the wilderness, and are dead. Your fathers they are, for ye are like them; murmuring sons of murmuring fathers. For in nothing did that people offend God more, than by their murmurs against Him. And therefore are they dead, because what they saw they believed, what they did not see they believed not, nor understood.

(Tr. xxvi. s. 12) This was the bread the manna typified, this was the bread the altar typified. Both the one and the other were sacraments, differing in symbol, alike in the thing signified. Hear the Apostle, They did all eat the same spiritual meat. (1 Cor. 10)

(Tr. xxvi. 11) But are we, who eat the bread that cometh down from heaven, relieved from death? From visible and carnal death, the death of the body, we are not: we shall die, even as they died. But from spiritual death which their fathers suffered, we are delivered. Moses and many acceptable of God, eat the manna, and died not, because they understood that visible food in a spiritual sense, spiritually tasted it, and were spiritually filled with it. And we too at this day receive the visible food; but the Sacrament is one thing, the virtue of the Sacrament another. Many a one receiveth from the Altar, and perisheth in receiving; eating and drinking his own damnation, (1 Cor. 11:29) as saith the Apostle. To eat then the heavenly bread spiritually, is to bring to the Altar an innocent mind. Sins, though they be daily, are not deadly. Before you go to the Altar, attend to the prayer you repeat: Forgive us our debts, as we forgive our debtors. (Matt. 6:12) If thou forgivest, thou art forgiven: approach confidently; it is bread, not poison. None then that eateth of this bread, shall die. But we speak of the virtue of the Sacrament, not the visible Sacrament itself; of the inward, not of the outward eater.

(Tr. xxvi. 13) was The manna too came down from heaven; but the manna was shadow, this is substance.

[AD 804] Alcuin of York on John 6:47-51
Therefore I say, He that eateth this bread, dieth not: I am the living bread which came down from heaven.

[AD 1107] Theophylact of Ohrid on John 6:47-51
(in v. 83) By becoming incarnate, He was not then first man, and afterwards assumed Divinity, as Nestorius fables.

[AD 373] Ephrem the Syrian on John 6:50
There remained yet another act that would abolish that Passover and would become the Passover of the Gentiles, a source of life until the end. Our Lord Jesus took bread in his hands, plain bread at the beginning, and blessed it, made the sign of the cross over it and sanctified it in the name of the Father and in the name of the Spirit, and he broke and distributed it in morsels to his disciples in his kindness. He called the bread his living body, and he filled it with himself and with his Spirit. He stretched forth his hand and gave them the bread that his right hand had sanctified: “Take, eat, all of you44 of this bread that my word has sanctified. Do not regard as bread what I have given you now … eat it, and do not disdain its crumbs. For this bread that I have sanctified is my body. Its least crumb sanctifies thousands of thousands, and it is capable of giving life to all who eat it. Take, eat in faith, doubting not at all that this is my body. And he who eats it in faith eats in it fire and the Spirit. If anyone doubts and eats it, it is plain bread to him. He who believes and eats the bread sanctified in my name, if he is pure, it will keep him pure; if he is a sinner, he will be forgiven. He, however, who despises it or spurns it, he may be sure that he is insulting the Son, who has called the bread his body and truly made it so. Receive of it, eat of it, all of you, and eat in it the Holy Spirit, for it is truly my body, and he who eats it will live forever. This is the heavenly bread that has come down from on high onto the earth. This is the bread that the Israelites ate in the wilderness and did not esteem. The manna that they gathered, which came down to them, was a figure of this spiritual bread that you have now received. Take and eat of it, all of you. In this bread you are eating my body. It is the true source of forgiveness.

[AD 397] Ambrose of Milan on John 6:50
I [Jesus] was not speaking previously about temporal life or death. Even if someone dies such a death, if he has taken my bread he will live forever. For he who proves himself, takes it. But he who takes it will not die the death of a sinner because this bread is the forgiveness of sins.

[AD 430] Augustine of Hippo on John 6:50
But are we, who eat the bread that comes down from heaven, relieved from death? From visible and carnal death, the death of the body, we are not: we shall die, even as they died. But from spiritual death, which their fathers suffered, we are delivered. Moses and … many who were acceptable to God ate the manna and did not die because they understood that visible food in a spiritual sense, spiritually tasted it and were spiritually filled with it. And we too on this day receive the visible food. But the sacrament is one thing, the virtue of the sacrament another. Many a one receives from the altar and perishes in receiving; eating and drinking his own damnation, as the apostle said. … To eat the heavenly bread spiritually then is to bring innocence to the altar. Though your sins are daily, at least let them not be deadly. Before you go to the altar, attend to the prayer you repeat, “Forgive us our debts, as we forgive our debtors.” If you forgive, you are forgiven: approach confidently; it is bread, not poison.… None then that eat of this bread shall die.