Cyril of Alexandria

Doth this offend you? what and if ye shall see the Son of Man ascend up where He was before? From utter ignorance, certain of those who were being taught by Christ the Saviour, were offended at His words. For when they heard Him saying, Verily, verily, I say unto you, except ye eat the Flesh of the Son of man and drink His Blood, ye have no life in you, they supposed that they were invited to some brutish savageness, as though they were enjoined to eat flesh and to sup up blood, and were constrained to do things- which are dreadful …

Commentary on the Gospel of John, Book 4 ↗

Theophylact of Ohrid

What then, if you see Me, in the appearance of the Son of Man, ascending into heaven, where I was before as God? For One and the Same ascends as Man to where He was before as God. He said this in order to draw them away from the opinion of Him as the son of Joseph. For whoever believed that He was formerly in heaven would undoubtedly also believe that He is the Son not of Joseph, but of God, and would ultimately believe His words as well. …

Commentary on John ↗

Augustine of Hippo

"Then what if ye shall see the Son of man ascending where He was before?" What is this? Did He hereby solve the question that perplexed them? Did He hereby uncover the source of their offense? He did clearly, if only they understood. For they supposed that He was going to deal out His body to them; but He said that He was to ascend into heaven, of course, whole: "When ye shall see the Son of man ascending where He was before;" certainly then, at least, you will see that not in the manner you suppose does He dispense His body; …

Tractates on John 27 ↗

Thomas Aquinas

Next, we see the kindly way Christ dispelled their difficulty. First, he takes notice of it; secondly, he removes its cause (v 63); and thirdly, he mentions what the cause was (v 65). He had noticed that they were scandalized because they had said, although privately, so he could not hear, This is a hard saying! But Christ, who in virtue of his divinity knew that they had said this, mentions it. …

Commentary on John ↗

Bonaventure

"If then you shall see the Son of man ascending where he was before" — the construction is incomplete — then you will know that the flesh is not to be divided into pieces, because the whole Christ will be entire in heaven: Augustine: "He is whole and entire in heaven; he remains entire under the Sacrament, he remains entire in your heart." Not only was their understanding false, but useless. …

Commentary on John, Chapter 6 ↗