John Chrysostom

"But if any man love God, the same," he doth not say, "knoweth Him," but, "is known of Him." For we have not known Him, but He hath known us. And therefore did Christ say, "Ye have not chosen Me, but I have chosen you." And Paul elsewhere, "Then shall I know fully, even as also I have been known." Observe now, I pray, by what means he brings down their high-mindedness. …

Homily on 1 Corinthians 20 ↗

Theophylact of Ohrid

These words have the following meaning: whoever loves his neighbor undoubtedly loves God as well; and whoever loves God (he did not say "has known" God, but) "has knowledge" from God, that is, has become known to God and His own. And having become known to God, he receives knowledge from Him; but even this knowledge is imperfect. Therefore, even if you do have knowledge, do not be puffed up: for it is not perfect and is not your own merit, but a gift from God. See how many measures he uses to restrain their arrogance.

Commentary on 1 Corinthians ↗

Augustine of Hippo

And the apostle: "if any man," he says, "think that he knoweth anything, he knoweth nothing yet as he ought to know. But if any man love God, the same is known of Him." He has not said, has known Him, which is dangerous presumption, but "is known of Him." So also in another place, when he had said, "But now after that ye have known God:" immediately correcting himself, he says, "or rather are known of God." And above all in that other place, "Brethren," he says, "I count not myself to have apprehended: but this one thing I do, …

On the Trinity 9.1 ↗