Theophylact of Ohrid

But now, he says, you have come to know God, or rather, it was not you who by your own effort found and came to know God (since you were not seeking at all), but He found you, living in darkness, and accepted you. For "you have been known" is said instead of "you have been accepted by God." How then do you turn back again to the weak and beggarly elements, that is, those having no power to obtain the promised blessings and unable to bring any spiritual benefit? …

Commentary on Galatians ↗

Ignatius of Antioch

For as one who has been thought worthy of a divine and desirable name, in those bonds which I bear about, I commend the Churches, in which I pray for a union both of the flesh and spirit of Jesus Christ, "who is the Saviour of all men, but specially of them that believe;" by whose blood ye were redeemed; by whom ye have known God, or rather have been known by Him; in whom enduring, ye shall escape all the assaults of this world: for "He is faithful, who will not suffer you to be tempted above that which ye are able."

Epistle of Ignatius to the Magnesians ↗

Oecumenius

"But now, having known God." For it is not you, he says, who find God by your own work, but He himself, while you were wandering in error, seized you. "how do you turn back again to," He discusses again concerning the sun and the moon and the stars, from which are the observations of the days. But he calls them poor and weak, as having no strength at all. The word "again" has much emphasis; after adoption, he says, and being known by God. — [CYRIL] Elements of the world, the particles of the entire cosmos. …

Commentary on Galatians ↗

Thomas Aquinas

Then when he says, "But now, after that you have known God, or rather are known by God," he reminds them of the gift received. As if to say: If you had been ignorant and sinned, it could have been tolerated; for other things being equal, sin in a Christian is more grievous than in a pagan. But now, since you have known God, i.e., were brought to a knowledge of God, you sin more gravely than of old by serving and setting your hope on things you ought not: "All shall know me, from the least of them even to the greatest" (Jer 31:34). …

Commentary on Galatians ↗