Augustine of Hippo — as excerpted in the Catena Aurea on John 6:60-71

“(Tr. xxvii. s. 10) He was elected to be an involuntary and unconscious instrument of producing the greatest good. For as the wicked turn the good works of God to an evil use, so reversely God turns the evil works of man to good. What can be worse than what Judas did? Yet our Lord made a good use of his wickedness; allowing Himself to be betrayed, that He might redeem us. In, Have I not chosen you twelve, twelve seems to be a sacred number used in the case of those, who were to spread the doctrine of the Trinity through the four quarters of the world. Nor was the virtue of that number impaired, by one perishing; inasmuch as another was substituted in his room.”