I am come into the world as a light. In order to render his disciples more bold and persevering, he proceeds still farther in maintaining the certainty of faith. And, first, he testifies that he came into the world to be a light, by which men might be delivered from darkness and errors; and, at the same time, he points out the means of obtaining so great a benefit, when he says, that whosoever believeth in me may not remain in darkness. Besides, he accuses of ingratitude all who, after having been taught by the Gospel, do not separate themselves from unbelievers; for the higher the excellence of this benefit, of being called from darkness to light, the less excusable are they who, through their indolence or carelessness, quench the light that had been kindled in them. The words, I am come into the world as a light, are highly emphatic; for though Christ was a light from the beginning, yet there is a good reason why he adorns himself with this title, that he has come to perform the part of a light. That we may perceive distinctly the various steps, he shows, first, that he is a light to others rather than to himself; secondly, that he is a light, not only to angels, but also to men; thirdly, that he was manifested in the flesh, in order that he might shine with full brightness. The term, whosoever, appears to have been added on purpose, partly, that all believers, without exception, may enjoy this benefit ill common, and partly, to show that the reason why unbelievers perish in darkness is, that, of their own accord, they forsake the light. Now, if the whole wisdom of the world were collected into one mass, not a single ray of the true light would be found in that vast heap; but, contrary, it will be a confused chaos; for it belongs to Christ alone to deliver us from darkness.

A light into the world - John 8:12; John 1:9; John 3:19.
Walk in darkness - In gross and dangerous errors. Darkness is put for error as well as for sin, John 3:19; 1-John 1:5. It is also used to denote the state when the comforts of religion are withdrawn from the soul, Isaiah 8:22; Joel 2:2; Isaiah 59:9; John 8:12.

I am come a light into the world - Probably referring to what his forerunner had said, John 1:5. Before the coming of this Savior, this sun of righteousness, into the world, all was darkness: at his rising the darkness is dispersed; but it only profits those whose eyes are open to receive the rays of this sun of righteousness. See on John 1:5 (note); John 3:19 (note); John 8:12 (note); John 9:5 (note).

I am come a light into the world,.... And even as the light of it, being the sun of righteousness, that was to arise, and now was risen, to enlighten men with the light of the living; see John 3:19;
that whosoever believeth on me should not abide in darkness; God's elect themselves, whilst in a state of unregeneracy and unbelief, are in darkness; when Christ shines in upon them, and infuses the light of faith into them, they are no longer in darkness; the darkness is past, at least in a great measure, and the true light shines; in which they see light, see glory and grace of Christ, and the invisible realities of another world: nor do they continue in the darkness of sin, ignorance, and unbelief; but walk in the light of truth, faith, and holiness, until the perfect day comes, when all the shadows of remaining darkness will flee away.