He says this as being the Head of the Church, of which we are the members, the Man Christ Jesus; for the vine and the branches are of the same nature. When He says, I am the true vine, He does not mean really a vine; for He is only called so metaphorically, not literally, even as He is called the Lamb, the Sheep, and the like; but He distinguishes Himself from that vine to whom it is said, How art thou turned into the degenerate plant of a strange vine unto me. (Jer. 11:21) For how is that a true vine, which when grapes are expected from it, produces only thorns?
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: Tr. lxxx. 2