Juan 15:5

I am the vine, ye are the branches
Christ here repeats what he said of himself, "the vine", for the sake of the application of "the branches" to his disciples: which expresses their sameness of nature with Christ; their strict and close union to him; and the communication of life and grace, holiness and fruitfulness, of support and strength, and of perseverance in grace and holiness to the end from him:

he that abideth in me, and I in him;
which is the case of all that are once in Christ, and he in them:

the same bringeth forth much fruit;
in the exercise of grace, and performance of good works; and continues to do so as long as he lives, not by virtue of his own free will, power, and strength, but by grace continually received from Christ:

for without me ye can do nothing;
nothing that is spiritually good; no, not anything at all, be it little or great, easy or difficult to be performed; cannot think a good thought, speak a good word, or do a good action; can neither begin one, nor, when it is begun, perfect it. Nothing is to be done "without Christ"; without his Spirit, grace, strength, and presence; or as "separate from" him. Were it possible for the branches that are truly in him, to be removed from him, they could bring forth no fruits of good works, any more than a branch separated from the vine can bring forth grapes; so that all the fruitfulness of a believer is to be ascribed to Christ, and his grace, and not to the free will and power of man.