18 At this point of my discourse I am truly filled with wonder at the wise dispensation of the Holy Spirit; how He confined the Epistles of the rest to a small number, but to Paul the former persecutor gave the privilege of writing fourteen. For it was not because Peter or John was less that He restrained the gift; God forbid! But in order that the doctrine might be beyond question, He granted to the former enemy and persecutor the privilege of writing more, in order that we all might thus be made believers. For all were amazed at Paul, and said, Is not this he that was formerly a persecutor? Did he not come hither, that he might lead us away bound to Jerusalem? Be not amazed, said Paul, I know that it is hard for me to kick against the pricks: I know that I am not worthy to be called an Apostle, because I persecuted the Church of God; but I did it in ignorance: for I thought that the preaching of Christ was destruction of the Law, and knew not that He came Himself to fulfil the Law and not to destroy it. But the grace of God was exceeding abundant in me.
Source: Catechetical Lectures (New Advent)