No conversion in sacred history is given so much attention as that of St. Paul. Besides the many references to it, we find three detailed accounts of it in the book of Acts. As Saul of Tarsus, the learned Pharisee, he had led his nation and the world in rebellion against God and the Lord Jesus Christ.
St. Luke says: “As for Saul, he made havock of the church” (Acts 8:3). The believers at Damascus feared Saul’s presence among them, saying: “Is not this he that destroyed them which called on this name in Jerusalem?” (Acts 9:21). Paul himself later testified: “Many of the saints did I shut up in prison…and when they were put to death, I gave my voice [vote] against them” (Acts 26:10). “…beyond measure I persecuted the church of God, and wasted it [laid it waste]” (Gal. 1:13).
There must have been an important reason why God saved this rebel leader. Clearly it was that He might make Paul, not only the herald, but the living example of “the exceeding riches of His grace” to sinners. Paul himself said:
“And I thank Christ Jesus our Lord…for…putting me into the ministry; who was before A BLASPHEMER, AND A PERSECUTOR, AND INJURIOUS: but I obtained mercy, because I did it ignorantly in unbelief. AND THE GRACE OF OUR LORD WAS EXCEEDING ABUNDANT….This is a faithful saying, and worthy of all acceptation, that CHRIST JESUS CAME INTO THE WORLD TO SAVE SINNERS, OF WHOM I AM CHIEF. HOWBEIT FOR THIS CAUSE I OBTAINED MERCY, THAT IN ME FIRST JESUS CHRIST MIGHT SHOW FORTH ALL LONGSUFFERING, FOR A PATTERN TO THEM WHICH SHOULD HEREAFTER BELIEVE ON HIM TO LIFE EVERLASTING” (I Tim.1:12-16). source