Augustine of Hippo
Catena Aurea · Johannesevangelium 15
Abide in me, and I in you. As the branch cannot bear fruit of itself, except it abide in the vine; no more can ye, except ye abide in me. I am the vine, ye are the branches: He that abideth in me, and I in him, the same bringeth forth much fruit: for without me ye can do nothing. If a man abide not in me, he is cast forth as a branch, and is withered; and men gather them, and cast them into the fire, and they are burned. If ye abide in me, and my words abide in you, ye shall ask what ye will, and it shall be done unto you.
(Tract. lxxxi. 3) But lest any should suppose that a branch could bring forth a little fruit of itself, He adds, For without Me ye can do nothing. He does not say, ye can do little. Unless the branch abides in the vine, and lives from the root, it can bear no fruit whatever. Christ, though He would not be the vine, except He were man, yet could not give this grace to the branches, except He were God.