Paul speaks to this and states that he was serving God ignorantly...I.E. he had no clue...his Pharisee(ism), unbelief and ignorance of the scriptures led him to erroneously do the things he had been doing......
English Standard Version
though formerly I was a blasphemer, persecutor, and insolent opponent. But I received mercy because I had acted ignorantly in unbelief,
Berean Study Bible
I was formerly a blasphemer, a persecutor, and a violent man; yet because I had acted in ignorance and unbelief, I was shown mercy.
Berean Literal Bible
being formerly a blasphemer, and a persecutor, and insolent; but I was shown mercy, because I did
it in unbelief, being ignorant.
New American Standard Bible
even though I was formerly a blasphemer and a persecutor and a violent aggressor. Yet I was shown mercy because I acted ignorantly in unbelief;
King James Bible
Who was before a blasphemer, and a persecutor, and injurious: but I obtained mercy, because I did
it ignorantly in unbelief.