Former Reputation Disregarded
1Tim 1:13 although I was formerly a blasphemer, a persecutor, and an insolent man; but I obtained mercy because I did it ignorantly in unbelief.
That is, Paul was not like an apostate. He was sincere in his persecution of the Church. He thought he was doing God's will. Not that his ignorance was an excuse. But rather to contrast himself with apostates for whom the Lord doesn't have mercy.
"For it is impossible for those who were once enlightened, and have tasted the heavenly gift, and have become partakers of the Holy Spirit, and have tasted the good word of God and the powers of the age to come, if they fall away, to renew them again to repentance, since they crucify again for themselves the Son of God, and put Him to an open shame." Heb 6:4-6
"For if we sin willfully after we have received the knowledge of the truth, there no longer remains a sacrifice for sin." Heb 10:26