John 15:3

(Tr. lxxx. 2) 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? (de Verb. Dom. serm. lix) For we cultivate God, and God cultivates us. But our culture of God does not make Him better: our culture is that of adoration, not of ploughing: His culture of us makes us better. His culture consists in extirpating all the seeds of wickedness from our hearts, in opening our heart to the plough, as it were, of His word, in sowing in us the seeds of His commandments, in waiting for the fruits of piety. (Tr. lxxx. 3) And who is there in this world so clean, that he cannot be more and more changed? Here, if we say that we have no sin, we deceive ourselves. (1 John 1:8) He cleanseth then the clean, i. e. the fruitful, that the cleaner they be, the more fruitful they may be. Christ is the vine, in that He saith, My Father is greater than I; but in that He saith, I and My Father are one, He is the husbandman; not like those who carry on an external ministry only; for He giveth increase within. Thus He calls Himself immediately the cleanser of the branches: Now ye are clean through the word, which I have spoken unto you. He performs the part of the husbandman then, as well as of the vine. But why does He not say, ye are clean by reason of the baptism wherewith ye are washed? Because it is the word in the water which cleanseth. […]

"I am," He says, "the true vine, and my Father is the husbandman. Every branch in me that beareth not fruit, He taketh away; and every one that beareth fruit, He purgeth it, that it may bring forth more fruit." Are, then, the husbandman and the vine one? Christ is the vine in the same sense as when He said, "The Father is greater than I;" but in that sense wherein He said, "I and my Father are one," He is also the husbandman. And yet not such a one as those, whose whole service is confined to external labor; but such, that He also supplies the increase from within. "For neither is he that planteth anything, neither he that watereth; but God that giveth the increase." But Christ is certainly God, for the Word was God; and so He and the Father are one: and if the Word was made flesh, that which He was not before, He nevertheless still remains what He was. And still more, after saying of the Father, as of the husbandman, that He taketh away the fruitless branches, and pruneth the fruitful, that they may bring forth more fruit, He straightway points to Himself as also the purger of the branches, when He says, "Now ye are clean through the word which I have spoken unto you." Here, you see, He is also the pruner of the branches, a work which belongs to the husbandman, and not to the vine; and more than that, He maketh the branches His workmen. For although they give not the increase, they afford some help; but not of themselves: "For without me," He says, "ye can do nothing." And listen, also, to their own confession: "What, then, is Apollos, and what is Paul but ministers by whom ye believed, even as the Lord gave to every man. I have planted, Apollos watered." And this, too, "as the Lord gave to every man;" and so not of themselves. […]

"Now ye are clean through the word which I have spoken unto you." Why does He not say, Ye are clean through the baptism wherewith ye have been washed, but "through the word which I have spoken unto you," save only that in the water also it is the word that cleanseth? Take away the word, and the water is neither more nor less than water. The word is added to the element, and there results the Sacrament, as if itself also a kind of visible word. For He had said also to the same effect, when washing the disciples' feet, "He that is washed needeth not, save to wash his feet, but is clean every whit." And whence has water so great an efficacy, as in touching the body to cleanse the soul, save by the operation of the word; and that not because it is uttered, but because it is believed? For even in the word itself the passing sound is one thing, the abiding efficacy another. "This is the word of faith which we preach," says the apostle, "that if thou shalt confess with thy mouth that Jesus is the Lord, and shalt believe in thine heart that God hath raised Him from the dead, thou shall be saved. For with the heart man believeth unto righteousness, and with the mouth confession is made unto salvation." Accordingly, we read in the Acts of the Apostles, "Purifying their hearts by faith;" and, says the blessed Peter in his epistle, "Even as baptism doth also now save us, not the putting away of the filth of the flesh, but the answer of a good conscience." "This is the word of faith which we preach," whereby baptism, doubtless, is also consecrated, in order to its possession of the power to cleanse. […]

He makes then His disciples a palpable and convincing demonstration of the art of the purifier of their souls; for already, He says, they are purged, not through a participation in anything else, but merely by the word spoken unto them, that is, the divine guidance of the Gospel. And this word proceeds from Christ. What man of sense, then, can any longer call in question that the Father has, as it were, a pruning-knife and hand, through whose instrumentality everything exists; that is, the Son, fulfilling the activity of that husbandry in us, which He attributes to the person of the Father, teaching us that all things proceed from the Father but by the instrumentality of the Son? For it is the Word of the Saviour that purgeth us, though the husbandry of our souls is attributed to God the Father. For this is His Living Word, sharp as a sword, piercing even to the dividing of soul and spirit, of both joints and marrow, and quick to discern the thoughts and intents of the heart. For, reaching into the depths of each man's inmost soul, and having every man's hidden purpose revealed before It as God, It brings Its keen edge to bear upon our vain pursuits by the working of the Spirit. For in this, I suppose, we shall deem our purification to consist. And all things that profit us in the attainment of virtue It increases and multiplies to bear the fruit which is conceived in righteousness.

"Now ye are clean through the word which I have spoken unto you." Seest thou how He introduceth Himself as tending the branches? "I have cleansed you," He saith; yet above He declareth that the Father doth this. But there is no separation between the Father and the Son.