Augustine of Hippo

And hence the same Apostle, even when he was still Saul, heard: "Saul, Saul, why do you persecute me?" because the body is joined to the head; and when already the preacher of Christ suffered from others the things which he himself had done as a persecutor: "To make up," he said, "what is lacking in the afflictions of Christ in my flesh," showing that what he suffered pertained to the afflictions of Christ. This cannot be understood concerning the head, which now in heaven suffers nothing of the sort, but concerning the body, that is, the Church, which body with its head is one Christ.