While—or, whensoever—I am in the world, I am the Light of the world. He had said (John 8:12), "I am the Light of the world: he that followeth me shall not walk in darkness." He was sublimely conscious of his power to do for the moral world what the sun was doing for the physical world.
He was the Occasion of its life, the Condition of its activity, the means of its instruction, the Source of all its beauty, its joy, and its progress. The ὅταν, which is translated quamdiu in the vulgate, and "so long as" in the Authorized version, means strictly "whensoever," and refers to the entire period of his activity (see John 1:5).
But while the sun of this world cannot open the eyes of the blind, and wastes his radiance on their sightless sockets, so, unless Christ were more than the sun, and could give the power as well as the opportunity of seeing, he would never have done the work of him that sent him.
The fact that he is the Light leads him to remind the disciples that he is the true Source of eyesight as well as of the conditions of vision. Light enough for all the world shines into the darkness, but the darkness comprehendeth it not.
This Jewish people are surrounded by floods of light. The spiritual world stands revealed fully to Christ's own gaze. But mankind hates the light, loves darkness on these matters rather than the light.
There is a radical fundamental change that must come over men, or they will never see. This evil, this terrible calamity that has befallen man, will vitiate all the provision of mercy. There must be a new beginning, a new birth, a work of God wrought in men, as well as a sublime revelation made to men, or the whole mission of the Christ would be incomplete.