"But for that reason I was shown mercy so that in me, the worst of sinners, Christ Jesus might

God doesn't choose human agents with impeccable credentials. Such persons would not answer his design. He picks individuals who are totally unqualified to represent him so that they become living advertisements for his great mercy. God is not a talent scout. He wants to be known for his unlimited patience, so that the world will know that there is hope and love for everyone.