Saint Augustine (354-430), bishop of Hippo (North Africa) and Doctor of the Church
Commentary on the Gospel of John, 80, 1, 81, 1:3-4; CCL 36, 527-531.
"I am the vine, you are the branches"
In the gospel passage where our Lord says he is the vine and his disciples the branches, and he speaks as head of the Church, and we its members. For "Christ is the mediator between God and men" (1 Tm 2:5). Indeed, the vine and the branches are the same nature, and why, because he was God, of a different nature than we, he became man so that human nature was in him like a vine we could be the branches.
He said to his disciples, "Abide in me and I in you. "They were not in him the same way it was in them. This reciprocal union do not procure any profit from them it is advantage. The branches are in the vineyard, not to enrich it, but to receive it the principle of their lives. The vineyard is in the branches, to communicate his life-giving, not to receive them. Thus the permanence of Christ's disciples, and the permanence of them in Christ, they are doubly advantageous, but not to Christ. Because if you subtract one branch, another may arise from the root remains alive, while the branch cut can not live separated from the root ...
If Christ was not a man, he would not have been the vine. However it does not provide this through the branches, if not also God. But, because without this grace, we can not live, because death is the power of our free will, our Lord says: "If anyone does not abide in me he is like a branch that was thrown out and withers. The branches dry, they are gathered, thrown into the fire and burned. "(Jn 15:6) Therefore, if the wood of the vine is even more contemptible when it does not remain in the vine, it is even more glorious when it remains so.