Ananias has just healed Saul/Paul of his blindness which happened at his conversion on the road to Damascus.
Acts 9 KJV
(20) And straightway he preached Christ in the synagogues, that he is the Son of God.
(21) But all that heard him were amazed, and said; Is not this he that destroyed them which called on this name in Jerusalem, and came hither for that intent, that he might bring them bound unto the chief priests?
It was Jews that accepted that Jesus as the Son of God, the promised Messiah of Israel, that Paul was persecuting.
Paul certainly wasn't persecuting them because they had a zeal for the law. Even Saul/Paul had a great zeal for the law before his conversion, so faith without the law was not something that Saul/Paul was persecuting because faith without law was not even being preached before Saul/Paul was converted.
Saul/Paul who once did not have faith that Jesus was the promised Messiah, the Son of GOD, now preached that He was.