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.
Mt. 6:22-23
When the eye is evil, the body becomes dark—not through the fault of the Creator, because everything God creates is good (Gen. 1:31), but according to the corrupt and malicious disposition of the one to whom the eye belongs. And you, wise reader, when you hear about the evil eye, do not understand it to be the eye in the head, but the evil thought in the unenlightened heart. And if it happens that the bodily eye will be darkened by severe suppuration and headache, then bodily blindness does not yet make a person alien to the benefits of the future and of eternity.
—St. Athanasius the Great. From Conversations on the Gospel of Matthew
The lamp for the body is the eye. So, if your eye is pure, then your whole body will be light.
Self-examination and prudence are an eye and a lamp for the soul, just as the eye is a lamp for the body.
And if the eye is light, then the whole body will be light, but if the eye is dark, then the whole body will be dark, as the Lord Himself said in the Gospel.
That is, through self-examination, a person examines and discerns all his desires, words, and actions, and shuns everything that can remove us from God.
With the help of this prudent discerning, man repels and completely eradicates all the tricks of the enemy and clearly distinguishes good from evil.
The truth of this is evident from the Holy Scriptures.
Because Saul, the king of Israel, did not have this lamp, his mind was so clouded that he did not even understand how to fulfill what God commanded him through Samuel the prophet, and that fulfilling this command would be better than offering a sacrifice. Therefore, he provoked God in the very thing that he thought to please Him, for which he was deprived of the kingdom (cf. 1 Kings 13, 7–15).
The Apostle calls this discernment, examination (cf. 1 Cor. 11, 28), and it is revered as the ruler and source of our life, according to this saying of Scripture: They that have no guidance fall like leaves: but in much counsel there is safety. (Proverbs 11:14).
That is, the Scripture calls self-examination advice, and instructs us not to do anything without advice; it does not even allow us without advice to drink spiritual wine, which makes a person’s heart glad, because it says: do nothing without advice (Sir. 32:19), Do all things with counsel: drink wine with counsel (Proverbs 31:3).
The same Scripture inspires us: just as а city without walls is destroyed, and into which anyone who wants can enter and plunder its treasures, so is a man who does without advice (Prov. 25:28 [Church Slavonic]).
—St. Anthony the Great. Answers to questions posed by the brethren.
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!
As the eyes are the light of the body, when the eyes are healthy then the whole body is illumined; but when something falls into the eyes and they are darkened, then the whole body abides in darkness—thus were the Apostles placed as the eyes and light for the whole world. Therefore, the Lord commanded them, saying, “If you, who are the light of the world, stand firm and do not become corrupted, then the whole body of the world will be illumined. But if you, the light of the world, are darkened, then how great will be “the darkness”—that is, the world? Thus the Apostles, who became the light, served as the light for those who believed, enlightening their hearts with that heavenly light of the Spirit by which they themselves were enlightened.
—St. Macarius the Great. Collected manuscripts, 2:1.
It is said: The light of the body is the eye (Mt. 6:22). For the higher thinking mind is the eye of the soul, and its sight greatly disperses its light upon all order of things. But if it is mmersed in unprofitable cares that drag it down into the abyss of destruction, if you lower your mind to what is coarse and pitiful, then will the mind be in a condition to imagine something good or suggest something profitable to its own thoughts? Therefore must all evil habits come to darkness and confusion that bring it, as in the night, perplexity and onerous struggle.
St. Nilus of Sinai. Letters on various topics, to Presbyter Serapion
