The key in this often used cliche is “by the grace of God” – Paul of course had a checkered past before his conversion; having had a partisan spirit towards the persecution of Christians. He met the One who he had been persecuted, and in a moment (you could say in the twinkling of an eye) he became God’s mouthpiece to the gentile world.
Paul writes in 1Corinthians 15 v10 “But by the grace of God I am what I am: and his grace which was bestowed upon me was not in vain; but I laboured more abundantly than they all: yet not I, but the grace of God which was with me.“
Paul is always quick to point out how fortunate he has been, to be given the ministry which he so faithfully upheld throughout his life – in the verses prior to v10 of 1Corinthians 15, he declares the gospel, by which we are saved, and proceeds to explain all the eyewitness accounts of those that had seen the resurrected Christ. He of course places himself last in this list, making the claim that “he is the least of the apostles” & “of one born out of due time“
Paul laid no claim to greatness or superiority towards others of his own accord, but because of the grace of God, he laboured more abundantly than the aforementioned eyewitnesses.
God’s grace can do wondrous things; it can save the most wretched of sinners from damnation, and in the context of 1Corinthians 15 v9-10, it can be the greatest motivation we need to accomplish great things for God ourselves…….AMAZING!! 
