Theophylact of Ohrid — as excerpted in the Catena Aurea on John 1:4

“He saith not, the Light of the Jews only, but of all men: for all of us, in so far as we have received intellect and reason, from that Word which created us, are said to be illuminated by Him. For the reason which is given to us, and which constitutes us the reasonable beings we are, is a light directing us what to do, and what not to do.”