What happened to Paul's personality after God saved him by grace?
God totally transformed and saved Paul by grace, yet his personality kept going. The intense zeal from his religious background was not destroyed but redirected: instead of using his energy to defeat the name of Christ, he now served out of love for Him, constrained and driven by the love of Christ.
Les explains that Paul's background as a religious zealot under Judaism set him up for this. His whole life had been wrapped up in Judaism and his work as a Pharisee. Even though God totally transformed the man and saved him by grace, that personality kept going. Now Paul turned all of that energy not to defeat the name of Christ but out of love for Him. The love of Christ constrained, or drove, him. Despite suffering inexorably for the Gospel and constantly defending his Apostleship against opposition, including Jewish people from Jerusalem who thought he was a false teacher and imposter, the love of Christ kept driving the man on.