
Gregory the Great
Catena Aurea · Matthäusevangelium 6
The light of the body is the eye: if therefore thine eye be single, thy whole body shall be full of light. But if thine eye be evil, thy whole body shall be full of darkness. If therefore the light that is in thee be darkness, how great is that darkness!
(Mor. xxviii. 11.) Otherwise; if the light that is in thee, that is, if what we have begun to do well, we overcloud with evil purpose, when we do things which we know to be in themselves evil, how great is the darkness!