John 15:4

"As the branch cannot bear fruit of itself except it abide in the vine, so neither can he who abideth not in Me." For that they might not be separated from Him by timidity, He fasteneth and glueth to Himself their souls slackened through fear, and holdeth out to them good hopes for the future. For the root remains, but to be taken away, or to be left, belongs to the branches. Then having urged them on in both ways, by things pleasant and things painful, He requireth first what is to be done on our side.

(Tract. lxxxi. 1) Abide in Me, and I in you: not they in Him, as He in them; for both are for the profit not of Him, but them. The branches do not confer any advantage upon the vine, but receive their support from it: the vine supplies nourishment to the branches, takes none from them: so that the abiding in Christ, and the having Christ abiding in them, are both for the profit of the disciples, not of Christ; according to what follows, As the branch cannot bear fruit of itself, except it abide in the vine, no more can ye, except ye abide in Me. Great display of grace! He strengtheneth the hearts of the humble, stoppeth the mouth of the proud. They who hold that God is not necessary for the doing of good works, the subverters, not the assertors, of free will, contradict this truth. For he who thinks that he bears fruit of himself, is not in the vine; he who is not in the vine, is not in Christ; he who is not in Christ, is not a Christian.

Jesus called Himself the vine, and His disciples the branches, and His Father the husbandman; whereon we have already discoursed as we were able. But in the present passage, while still speaking of Himself as the vine, and of His branches, or, in other words, of the disciples, He said, "Abide in me, and I in you." They are not in Him in the same kind of way that He is in them. And yet both ways tend to their advantage, and not to His. For the relation of the branches to the vine is such that they contribute nothing to the vine, but from it derive their own means of life; while that of the vine to the branches is such that it supplies their vital nourishment, and receives nothing from them. And so their having Christ abiding in them, and abiding themselves in Christ, are in both respects advantageous, not to Christ, but to the disciples. For when the branch is cut off, another may spring up from the living root; but that which is cut off cannot live apart from the root.

And then He proceeds to say: "As the branch cannot bear fruit of itself, except it abide in the vine; no more can ye, except ye abide in me." A great encomium on grace, my brethren, one that will instruct the souls of the humble, and stop the mouths of the proud. Let those now answer it, if they dare, who, ignorant of God's righteousness, and going about to establish their own, have not submitted themselves unto the righteousness of God. Let the self-complacent answer it, who think they have no need of God for the performance of good works. Fight they not against such a truth, those men of corrupt mind, reprobate concerning the faith, whose reply is only full of impious talk, when they say: It is of God that we have our existence as men, but it is of ourselves that we are righteous? What is it you say, you who deceive yourselves, and, instead of establishing freewill, cast it headlong down from the heights of its self-elevation through the empty regions of presumption into the depths of an ocean grave? Why, your assertion that man of himself worketh righteousness, that is the height of your self-elation. But the Truth contradicts you, and declares, "The branch cannot bear fruit of itself, except it abide in the vine." Away with you now over your giddy precipices, and, without a spot whereon to take your stand, vapor away at your windy talk. These are the empty regions of your presumption. But look well at what is tracking your steps, and, if you have any sense remaining, let your hair stand on end. For whoever imagines that he is bearing fruit of himself is not in the vine, and he that is not in the vine is not in Christ, and he that is not in Christ is not a Christian. Such are the ocean depths into which you have plunged.