Augustine of Hippo

So note how this Saul, later Paul, ironically "congratulates himself" on having attained to the mercy of God, because he was found to be the first, that is the most outstanding, in sins!… This was so that others could all say to themselves, "if Paul was cured, why should I despair? If such a desperately sick man was cured by such a great physician, who am I, not to fit those hands to my wounds, not to hasten to the care of those hands?" That people might be able to say that sort of thing, that's why Saul was made into an apostle out of a persecutor. When a doctor comes to a new place, he looks for someone there who's been despaired of and cures him, even if he finds he's very poor, provided he finds him a desperate case. He is not looking for a fee but displaying his skill.