John Chrysostom

God indeed says that he called Paul on account of his excellent capacity, as he said to Ananias, "for he is a chosen instrument of mine to carry my name before the Gentiles and kings." That is to say, he was capable of service and the accomplishment of great deeds. God gives this as the reason for his call. But Paul himself everywhere ascribes it to grace and to God's inexpressible mercy. He says this in the words, "I received mercy for this reason, that in me, as the foremost, Jesus Christ might display his perfect patience for an example to those who were to believe in him for eternal life."