John Gills Exposition of the Bible Commentary

Verse 4 (John 15:4)

Abide in me, and I in you ,.... The former of these is an exhortation to continue in the exercise of faith and love upon Christ, holding to him the head, cleaving to him with full purpose of heart, and so deriving life, grace, strength, and nourishment from him; the latter is a promise encouraging to the former; for as Christ is formed in the hearts of his people, he continues there as the living principle of all grace. And so,

as the branch cannot bear fruit of itself, except it abide in the vine, no more can ye, except ye abide in me ; which strongly expresses the necessity of abiding in Christ by fresh repeated acts of faith: and it is easy to observe, that when believers depart from Christ, though it be but partially, and for a time, for they cannot finally and totally depart from him, in what a poor, withered, fruitless condition they are, both in their frames and duties.

- John Gills Exposition of the Bible Commentary