Augustine of Hippo — as excerpted in the Catena Aurea on John 12:44-50

“(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.”