Luke 11:35

That is, If thy material body, when the light of a candle shines upon it, is made full of light, so that not one of thy members is any longer in darkness; much more when thou sinnest not, shall thy whole spiritual body be so full of light, that its brightness may be compared to the shining of a candle, while the light which was in the body, and which used to be darkness, is directed whithersoever the understanding may command.

(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.

(de Cons. Ev. lib. ii. c. 39.) Luke indeed relates this in the same place as Matthew, but in a somewhat different order. But who does not see that it is an idle question, in what order our Lord said those things, seeing that we ought to learn by the most precious authority of the Evangelist, that there is no falsehood. But not every man will repeat another's words in the same order in which they proceeded from his mouth, seeing that the order itself makes no difference with respect to the fact, whether it be so or not.

(28. Mor. c. 12.) Or else; By the name body each particular action is understood which follows its own intention, as it were the eye of the spectators. Therefore it is said, The light of the body is the eye, because by the ray of a good intention the deserving parts of an action receive light. If then thy eye be single, thy whole body will be full of light, for if we intend rightly in singleness of heart, we accomplish a good work, even though it seem not to be good. And if thy eye be evil, thy whole body will be full of darkness, because when with a crooked intention even a right thing is done, although it appears to glitter in men's sight, yet before the bar of the internal judge it is covered with darkness. Hence too it is rightly added, Take heed therefore that the light which is in thee be not darkness. For if what we think we do well we cloud by a bad intention, how many are the evils themselves which even when we do them we know to be evil?

But as if the eye of the body be light the body will be light, but if dark the body will be dark also, so is it with the understanding in relation to the soul. Hence it follows, If thine eye be single, thy whole body will be full of light; but if evil, thy whole body will be full of darkness.