1 In this chapter of the Gospel, brethren, our Lord Jesus Christ has most especially commended Himself to our faith in respect of His humanity. For indeed He always keeps in view, both in His words and deeds, that He should be believed to be God and man: God who made us, man who sought us; with the Father, always God; with us, man in time. For He would not have sought man whom He had made if Himself had not become that which He had made. But remember this, and do not let it slip from your hearts, that Christ became man in such manner that He ceased not to be God.
While remaining God, He who made man took manhood. While, therefore, as man He concealed Himself, He must not be thought to have lost His power, but only to have offered an example to our infirmity. For He was detained when He willed to be, and He was put to death when he willed to be. But since there were to be His members, that is, His faithful ones, who would not have that power which He, our God, had; by His being hid, by His con cealing Himself as if He would not be put to death, He indicated that His members would do this, in which members He Himself in fact was.
For Christ is not simply in the head and not in the body, but Christ whole is in the head and body. What, therefore, His members are, that He is; but what He is, it does not necessarily follow that His members are. For if His members were not Himself, He would not have said, “Saul, why do you persecute me?” For Saul was not persecuting Himself on earth, but His members, namely, His believers. He would not, however, say, my saints, my servants, or, in short, my brethren, which is more honorable; but, me, that is, my members, whose head I am.
Source: Tractates on the Gospel of John (New Advent)