John 12:46

"I am come a light into the world." For since the Father is called by this name everywhere both in the Old Testament and in the New, Christ useth the same name also; therefore Paul also calleth Him, "Brightness" (Heb. i. 3), having learnt to do so from this source. And He showeth here His close relationship with the Father, and that there is no separation between them, if so be that He saith that faith on Him is not on Him, but passeth on to the Father. And He called Himself "light," because He delivereth from error, and dissolveth mental darkness.

(Tr. liv. 4) Whereby it is evident, that He found all in darkness. In which darkness if they wish not to remain, they must believe in the light which is come into the world. He says in one place to His disciples, Ye are the light of the world; but He did not say to them, Ye are come a light into the world, that whosoever believeth on you should not abide in darkness. All saints are lights, but they are so by faith, because they are enlightened by Him, from Whom to withdraw is darkness.

Attend to what follows: "I am come a light into the world, that whosoever believeth on me should not abide in darkness." He said in a certain place to His disciples, "Ye are the light of the world. A city that is set on a hill cannot be hid. Neither do men light a candle, and put it under a bushel, but on a candlestick; that it may give light to all that are in the house: so let your light shine before men, that they may see your good works, and glorify your Father who is in heaven:" but He did not say to them, Ye are come a light into the world, that whosoever believeth on you should not abide in darkness. Such a statement, I maintain, can nowhere be met with. All the saints, therefore, are lights, but they are illuminated by Him through faith; and every one that becomes separated from Him will be enveloped in darkness. But that Light, which enlightens them, cannot become separated from itself; for it is altogether beyond the reach of change. We believe, then, the light that has thus been lit, as the prophet or apostle: but we believe him for this end, that we may not believe on that which is itself enlightened, but, with him, on that Light which has given him light; so that we, too, may be enlightened, not by him, but, along with him, by the same Light as he. And when He saith, "That whosoever believeth on me may not abide in darkness," He makes it sufficiently manifest that all have been found by Him in a state of darkness: but that they may not abide in the darkness wherein they have been found, they ought to believe on that Light which hath come into the world, for thereby was the world created.