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!
When the eye is evil the body becomes dark, but the Creator is not to blame for this—because everything that God has made is very good (cf. Gen. 1:31)—but rather the corrupt and ill-intentioned morals of the one to whom the eye belongs. And you, wise reader, in hearing about the evil eye understand it to be not the eye in the head, but the evil thoughts in the unenlightened heart. And if it so happens that the bodily eye can become darkened by strong suppurations and from headaches, physical blindness nevertheless does not make a man foreign to future and eternal blessedness.
From his Discourses on the Gospel of Matthew.
The light of the body is the eye: if therefore thine eye be single, thy whole body shall be full of light.
Self-examination and prudence is the eye and lamp of the soul, just as the eye is the lamp of the body.
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!
That is, through self-examination a person searches and discerns all his desires, words, and actions and avoids all that can separate him from God.
With the help of this wise discernment a person deflects and completely destroys all the enemy’s deceit and clearly discerns good from evil.
The truth of this is clear in Holy Scripture.
Because Saul the king of Israel did not have this lamp, his mind became so darkened that he did not even understand how to fulfill what God commanded him through the prophet Samuel and that the fulfillment of these commandments would be better than making sacrifices; therefore he irritated God by the very thing that he thought would please Him. For this his kingdom was taken from him (cf. 1 Kings 13:7–15).
The apostle calls this discernment “examining himself” (cf. 1 Cor. 11:28), and it is honored as the ruler and source of our life, according to the Scripture: They that have no guidance fall like leaves: but in much counsel there is safety (Prov. 11:14).
That is, the Scripture calls self-examination counsel and prescribes it to us so that we would do nothing without counsel; it does not even allow us without counsel to drink spiritual wine that makes the heart glad, for it says, Do nothing without advice (Sir. 36:31), Do all things with counsel: drink wine with counsel (Prov. 26:3).
The same scripture tells us, As a city whose walls are broken down, and which is unfortified, in which, that is, anyone can come in and pilfer as he pleases, so is a man who does anything without counsel (Prov. 27:28).
Answers to questions posed by the brothers.
The eyes are the light of the body, and when the eyes are healthy, the whole body is illuminated; and when something gets into the eyes and they are darkened, the whole body is in darkness—so were the apostles placed as the eyes and light for the whole world. Therefore, the Lord commanded them, “If you will be the light of the world, stand steadfast and do not lie, then the body of the world will be enlightened. But if you—the light of the world—are darkened, then “that darkness will be great”—that is, the world. Thus, having become light, the apostles received light for those who believed, enlightening their hearts with the heavenly light of the Spirit with which they themselves were enlightened.
Collected manuscripts, type II. Discourse 1.
It is said, the light of the body is the eye (Matt. 6:22). For the mind that has its thoughts on high is the eye of the soul, and its sight strongly disseminates its light throughout the construct of all things. But if drunken amidst useless cares that draw the mind downward into the abyss of destruction you incline your mind to what is coarse and pitiful, then will the mind be in any shape to present itself as something good, or to suggest something profitable to its own thoughts? Therefore every evil habit, which everywhere, like at night, brings the mind perplexity and onerous struggle, necessarily leads to darkness and confusion.
Letters on various themes. To Priest Serapion.
What other eye does He mean here other than the mind? This eye can be simple if it sees simple (pure) light. Simple (pure) light is Christ. Thus, whoever has in himself the light of Christ, which would shine in his mind, about him it is said that he has the mind of Christ. When your eye, that is, the mind, is simple, that is, shines, then your bodiless body, that is, all the parts of your soul, will be light; and to the contrary, when your mind is evil, that is, darkened and extinguished, then your whole soul will be dark. Thus, think well—is darkness or light in you? Think deeply also—do you not think that you possess what you have not yet begun to acquire? Look well at this, that you might not be deceived and think that you have light in you when it is not light, but darkness.
Homilies (Homily 59).
God is the All-Seeing Eye—and our souls are simple (the Church Slavonic word prostiy, meaning open, forthright, pure; whole, not divided into parts); for if your eye shall be simple, your whole body will be light, says the Lord. Thus, may your eye be the Lord in your heart. Our soul is the eye that comes from the Eye, and as the soul sees through bodily vision, so does God—the Eye of our heart—see through the eye of our heart in its pure state. This is how the prophets and clairvoyant saints saw what is in the future and hidden, and the hidden thoughts of man.
Diary. Vol XI.
From the website of Optina Monastery