Life of itself gives illumination to men, but to cattle not: for they have not rational souls, by which to discern wisdom: whereas man, being made in the image of God, has a rational soul, by which he can discern wisdom. Hence that life, by which all things are made, is light, not however of all animals whatsoever, but of men.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: in Joh. tr. 1. c. 18