Theophylact of Ohrid
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.
Or else, because the Jews, seeing the miracles, accused them out of the malice of their heart, therefore our Lord tells them, that, receiving the light, that is, their understanding, from God, they were so darkened with envy, as not to recognise His miracles and mercies. But to this end received we our understanding from God, that we should place it upon a candlestick, that others also who are entering in may see the light. The wise man indeed has already entered, but the learner is still walking. As if He said to the Pharisees, You ought to use your understanding to know the miracles, and declare them to others, seeing that what you see are the works not of Beelzebub, but the Son of God. Therefore, keeping up the meaning, He adds, The light of the body is the eye.