John Chrysostom

"And I was still unknown by face unto the Churches of Judaea; but they only heard say, he that once persecuted us now preacheth the faith of which he once made havoc." What modesty in thus again mentioning the facts of his persecuting and laying waste the Church, and in thus making infamous his former life, while he passes over the illustrious deeds he was about to achieve! …

Homily on Galatians 1 ↗

Theophylact of Ohrid

Therefore, he says, the Christians in Judea did not even know me by face. So how could I have preached circumcision to them, when they did not even know me by face? For they slandered him, saying that in Judea he preached circumcision.

Commentary on Galatians ↗

Oecumenius

"I was unknown." Therefore, he says, I did not preach to those who had believed from the circumcision that they must be circumcised (for this is what the slanderers said, that he proclaimed circumcision to those who believed from the Jews); therefore I did not preach, he said, since they did not know from the beginning. Or therefore. — [PHOTIUS] From Peter I did not learn; I only saw him. From James I did not learn; for I only saw him as well. I did not see any other of the apostles. …

Commentary on Galatians ↗

Jerome

But I was unknown by face to the churches of Judea, which were in Christ Jesus. They only heard it said: He who once persecuted us now preaches the faith which he once tried to destroy. And they glorified God in me. The churches of Judea had only heard of me by reputation. And among them, they saw me more as a persecutor than as an apostle. …

Commentary on Galatians ↗

Thomas Aquinas

Secondly, how he was known by the others, namely, not by sight but by report and reputation. Hence he says, "I was unknown by face to the churches of Judea, which were in Christ," i.e., in the faith of Christ: "As unknown and yet known" (2 Cor 6:8). Hence it is evident that the churches of Judea did not teach me.

Commentary on Galatians ↗