Cyril of Alexandria

Ye have just said (He saith) When Christ cometh, no man knoweth whence He is. But since ye insist that ye hold this your opinion rightly, as being the truth, I agree to your words herein. For True is He of Whom I am, the Father, but He is not known of you. …

Commentary on the Gospel of John, Book 5 ↗

Theophylact of Ohrid

"I know Him," for knowing Him, neither evil intention nor deeds contrary to Him hinder Me. "Because I am from Him," that is, from Him, not from another essence, not foreign to Him. "And He sent Me." Here two natures in Christ are clearly indicated: by the words "I am from Him" – the divine Nature, and by the words "and He sent Me" – the human. For the Son of God is called an Envoy, as well as a Servant of God, according to His humanity.

Commentary on John ↗

Augustine of Hippo

Lastly, to show whence they could get to know Him (who had sent Him), He adds, I know Him: so if you would know Him, enquire of Me. No one knoweth the Father, save the Son, and he to whom the Son will reveal Him. And if I should say, I know Him not, I should be a liar like unto you. (c. 8:55) (Tr. xxxi. 4) I am from Him, He says, i. e. as the Son from the Father: but that you see Me in the flesh is because He hath sent Me. Wherein understand not a difference of nature, but the authority of a father.

Catena Aurea by Aquinas ↗

Hilary of Poitiers

I ask however, does the being from Him express a work of creation, or a birth by generation? If a work of creation, then every thing which is created is from Him. And how then does not all creation know the Father, if the Son knows Him, because He is from Him? But if the knowledge of the Father is peculiar to Him, as being from Him, then the being from Him is peculiar to Him also; i. e. the being the true Son of God by nature. So you have then a peculiar knowledge springing from a peculiar generation. …

Catena Aurea by Aquinas ↗

Thomas Aquinas

Then when he says, I know him, he teaches us how to know him from whom he is. For if a thing is to be learned, it must be learned from one who knows it. But only the Son knows the Father. And so he says: If you wish to know him who sent me, you must acquire this knowledge from me, because I alone know him. First, he shows that he knows him; secondly, he shows the perfection of his knowledge; and thirdly, the nature of his knowledge. He shows that he knows him when he says, I know him. …

Commentary on John ↗