Cyril of Alexandria

Common now to all is the word which seals the faith of Nathanael. But in saying that angels shall be seen speeding up and down upon the Son of Man, that is, ministering and serving His commands, for the salvation of such as shall believe, He says that then especially shall He be revealed as being by Nature Son of God. For it is not one another that the rational powers serve but surely God. And this does not take away subjection among the angels (for this will not be reasonably called bondage). …

Commentary on the Gospel of John, Book 2 ↗

Theophylact of Ohrid

Therefore the Lord also, correcting him and leading him to an understanding worthy of His Divinity, says: you will see the angels of God ascending and descending upon the Son of Man. "Accept Me," He says, "not as a mere man, but as the Master of angels." For He whom the angels serve cannot be a mere man, but is true God. This was fulfilled at the crucifixion and at the ascension. …

Commentary on John ↗

Augustine of Hippo

Let us recollect the Old Testament account. Jacob saw in a dream a ladder reaching from earth to heaven; the Lord resting upon it, and the angels ascending and descending upon it. Lastly, Jacob himself understanding what the vision meant, set up a stone, and poured oil upon it. (Gen. 28:12.) When he anointed the stone, did he make an idol? No: he only set up a symbol, not an object of worship. Thou seest here the anointing; see the Anointed also. He is the stone which the builders refused. …

Catena Aurea by Aquinas ↗

Thomas Aquinas

And accordingly he says, Amen, amen, I say to you, you will see the heavens opened and the angels of God ascending and descending on the Son of Man. By this, according to Chrysostom, the Lord wishes to prove that he is the true Son of God, and God. For the peculiar task of angels is to minister and be subject: "Bless the Lord, all of you, his angels, his ministers, who do his will" (Ps 102:20). So when you see angels minister to me, you will be certain that I am the true Son of God. …

Commentary on John ↗

Bonaventure

"And he says to him: Amen, amen I say to you, that you will see heaven opened," according to what is said in Matthew chapter three, that John saw that the heavens were opened over him. "And the Angels of God ascending and descending upon the Son of man." Literally, Angels descended to him, according to what is said in Matthew chapter four: "Angels came and ministered to him"; spiritually however, as Augustine says, what was said to Nathanael is now fulfilled in Christians, because after God-made-man ascended, the entrance to heaven …

Commentary on John, Chapter 1 ↗