Albert Barnes Commentary Galatians 1:23

"but they only heard say, He that once persecuted us now preacheth the faith of which he once made havoc;" — Galatians 1:23 (ASV)

But they had heard only, etc. They had not seen me; but the remarkable fact of my conversions had been reported to them. It was a fact that they could hardly be concealed. (See Acts 26:26.)