John Chrysostom
Catena Aurea · Lukasevangelium 11
No man, when he hath lighted a candle, putteth it in a secret place, neither under a bushel, but on a candlestick, that they which come in may see the light. The light of the body is the eye: therefore when thine eye is single, thy whole body also is full of light; but when thine eye is evil, thy body also is full of darkness. Take heed therefore that the light which is in thee be not darkness. If thy whole body therefore be full of light, having no part dark, the whole shall be full of light, as when the bright shining of a candle doth give thee light.
(Hom. 20. in Matt.) If then we have corrupted the understanding, which is able to let loose the passions, we have done violence to the whole soul, and suffer dreadful darkness, being blinded by the perversion of our understanding. Therefore adds he, Take heed, therefore, that the light which is in thee be not darkness. He speaks of a darkness which may be perceived, but which has its origin within itself, and which we every where carry about with us, the eye of the soul being put out. Concerning the power of this light He goes on to say, If thy whole body therefore be full of light, &c. &c.