"Cum autem plácuit Deo, qui me segregávit de útero matris meæ et vocávit per grátiam suam, ut reveláret Fílium suum in me...." ["But when he who had set me apart before I was born, and had called me through his grace, was pleased to reveal his Son to me...."]
God's grace was operative in St. Paul from before he was born. He was a vessel of election (see my next post). Of course, according to Paul himself the covenant of Moses was a grace, but I will presume he meant more than that. Paul's zealousness and devotion for the Law was part of his long preparation for receiving the revelation of Christ when it occurred. The difference wasn't the operation of grace, but Paul's awareness or consciousness of that operation. We often focus so much on the bad that is happening in our lives, that we are unaware, or blind to the operation of grace, or divine providence. That is why the Ignatian Examine begins with thanksgiving and includes meditation on the operation of grace in your life during that day.