John 9:5

5.While I am in the world, I am the light of the world. I consider this to have been added, by way of anticipation; for it might have been thought strange that Christ should speak of his time of working as limited, as if there were danger that the night should come upon him by surprise, as it does on other men. Thus, while he makes a distinction between himself and others, still he says that his time of working is limited. For he compares himself to the sun which, though it illuminates the whole earth by its brightness, yet, when it sets, takes away the day along with it. In this manner he states that his death will resemble the setting of the sun; not that his death extinguishes or obscures his light, but that it withdraws the view of it from the world. At the same time, he shows that, when he was manifested in flesh, that was truly the time of the day-light of the world. For though God gave light in all ages, yet Christ, by his coming, diffused a new and unwonted splendor. Hence he infers that this was an exceedingly fit and proper time, and that it might be said to be a very bright day, for illustrating the glory of God, when God intended to make a more striking exhibition of himself in his wonderful works.

But here arises another question. After the death of Christ, the power of God shone more illustriously, both in the fruit of the doctrine and in miracles; and Paul applies this strictly to the time of his own preaching, that

God, who from the beginning of the world commanded the light to shine out of darkness, at that time shone in the face of Christ by the Gospel,
(2 Corinthians 4:6.)

And does Christ now give less light to the world than when he was in the presence of men, and conversed with them? I reply, when Christ had finished the course of his office, he labored not less powerfully by his ministers than he had labored by himself, while he lived in the world. This I acknowledge to be true; but, first, it is not inconsistent with what he had said, that he was bound to perform, in his own person, what had been enjoined on him by the Father, and at the time when he was manifested in the flesh for that purpose. Secondly, it is not inconsistent with what he said, that his bodily presence was the true and remarkable day of the world, the lustre of which was diffused over all ages. For whence did the holy fathers in ancient times, or whence do we now, desire light and day, but because the manifestation of Christ always darted its rays to a great distance, so as to form one continued day? Whence it follows, that all who have not Christ for their guide grope in the dark like the blind, and wander about in confusion and disorder. Yet we must hold by this meaning of the words, that, as the sun discovers to our view the lovely spectacle of earth and heaven, and the whole arrangement of nature, so God has visibly displayed the chief glory of his works in his Son.