Jesus Christ · The Sermon on the Mount
The Eye as the Lamp of the Body
“The light of the body is the eye.” A short, strange-sounding saying — until you notice where Jesus put it. It sits between two teachings about money: lay up treasure in heaven (6:19–21) just before, cannot serve God and mammon (6:24) right after. In that placement, a “sound” eye and an “evil” eye are not first about eyesight. They are about what a person is looking at — and what a person is willing to let go of.
The Text
— Matthew 6:22–23The eye is the lamp of the body. If your eyes are good, your whole body will be full of light.A single, sound eye — the whole body full of light.
But if your eyes are bad, your whole body will be full of darkness. If then the light within you is darkness, how great is that darkness!An evil eye — the whole body full of darkness.
These two verses stand between two sayings about money — “lay not up for yourselves treasures upon earth” just before them (6:19–21), and “ye cannot serve God and mammon” right after (6:24). They are not a detour into eye health. They are the hinge that connects the two.
The Lamp Optics
— what a single eye and an evil eye each fill the body withA SINGLE EYE — MATTHEW 6:22
“thy whole body shall be full of light”
AN EVIL EYE — MATTHEW 6:23
“thy whole body shall be full of darkness”
What He Is Saying
— two readings, kept togetherIn everyday speech, an eye does not make light — it lets light in, or shuts it out. Jesus takes that ordinary fact and turns it into a picture of the whole inner life: what a person fixes their eye on decides whether they are full of light or full of darkness. The word for “single” is the Greek haplous — simple, sound, undivided. The question the saying asks is what the eye is undivided about.
Reading one: the generous eye and the grasping eyethe Hebrew idiom
In Hebrew idiom, a “good eye” describes a generous person and an “evil eye” describes a stingy or envious one — the same picture behind Proverbs' warnings against the grudging giver and the man “that hasteth to be rich.” Read this way, Jesus's single eye is the generous eye: a life that gives freely fills up with light. A grasping eye — hoarding, envying, calculating what it can keep — darkens everything it touches. That reading is increasingly where scholars land, and it explains the placement exactly: treasure in heaven, then the eye, then God-or-mammon — three sayings on the same subject in a row.
Reading two: the eye as the window of the soulthe older reading
An older reading, carried in much of the church's historic commentary, takes the eye more broadly — as the window through which spiritual light or spiritual darkness enters the whole person. On this reading “single” means an undivided intention, a heart not split between two objects. A divided inner eye lets in confusion and shadow no matter how the outward life looks. Neither reading cancels the other — the same Greek word carries both, and the church has heard both for centuries.
Both readings land on the same warning: “if the light that is in thee be darkness, how great is that darkness.” A grasping heart mistakes its own grasping for clear sight — the very organ meant to let light in has itself gone dark, and it does not know it.
The Voices on the Sound Eye
— the church hears Matthew 6:22The light--rather, "the lamp." of the body is the eye: if therefore thine eye be single--simple, clear. As applied to the outward eye, this means general soundness; particularly, not looking two ways. Here, as also in classical Greek, it is used figuratively to denote the simplicity of the mind's eye, singleness of purpose, looking right at its object, as opposed to having two ends in view.
Jamieson, Fausset & Brown· Commentary Critical and Explanatory on the Whole Bible (1871), Matt 6:22
The light of the body is the eye - That is, the eye is to the body what the sun is to the universe in the day time, or a lamp or candle to a house at night.
Adam Clarke· Commentary on the Bible (1832), Matt 6:22
We know that all our works are pure and pleasing in the sight of God if they are performed with a single heart. This means that they are performed out of charity and with an intention that is fixed on heaven. For "love is the fulfillment of the law." Therefore in this passage we ought to understand the eye as the intention with which we perform all our actions. If this intention is pure and upright and directing its gaze where it ought to be directed, then unfailingly all our works are good works, because they are performed in accordance with that intention. And by the expression "whole body," Christ designated all those works that he reproves and that he commands us to put to death. For the apostle also designates certain works as our "members." "Therefore," Paul writes, "mortify your members which are on earth: fornication, uncleanness, covetousness," and all other such things.
Augustine of Hippo· Sermon on the Mount 2.13.45 (430), on Matt 6:22
The Voices on the Evil Eye
— the church hears Matthew 6:23But if thine eye be evil--distempered, or, as we should say, If we have got a bad eye. thy whole body shall be full of darkness--darkened. As a vitiated eye, or an eye that looks not straight and full at its object, sees nothing as it is, so a mind and heart divided between heaven and earth is all dark.
Jamieson, Fausset & Brown· Commentary Critical and Explanatory on the Whole Bible (1871), Matt 6:23
This is an illustration drawn from the senses. As the whole body is in darkness, where the eye is not single, so if the soul has lost her original brightness, every sense, or that whole part of the soul to which sensation belongs, will abide in darkness. Wherefore He says, If then the light which is in thee be darkness, how great is that darkness! that is, if the senses which are the soul's light be darkened by vice, in how great darkness do you suppose the darkness itself will be wrapped?
Jerome· Catena Aurea by Aquinas (420), on Matt 6:22–23
Otherwise; from the office of the light of the eye, He calls it the light of the heart; which if it continue single and brilliant, will confer on the body the brightness of the eternal light, and pour again into the corrupted flesh the splendor of its origin, that is, in the resurrection. But if it be obscured by sin, and evil in will, the bodily nature will yet abide subject to all the evils of the understanding.
Hilary of Poitiers· Catena Aurea by Aquinas (367), on Matt 6:22–23
Where It Points
— the same eye, elsewhere in ScriptureA generous man will be blessed, for he shares his bread with the poor.“He that hath a bountiful eye” — the good eye named as generosity.
Be careful not to harbor this wicked thought in your heart: “The seventh year, the year of release, is near,” so that you look upon your poor brother begrudgingly and give him nothing. He will cry out to the LORD against you, and you will be guilty of sin.The warning against “thine eye be evil against thy poor brother.”
Do I not have the right to do as I please with what is mine? Or are you envious because I am generous?’“Is thine eye evil, because I am good?” — Jesus uses the same idiom of envy at the wage in His own parable.
Deuteronomy and Proverbs give the idiom its Old Testament home — the good eye is the open hand, the evil eye is the grudging one that begrudges a brother in need. Jesus uses the same phrase Himself in the Parable of the Workers: the all-day laborers grumble at the landowner's generosity to latecomers, and he answers, “is thine eye evil, because I am good?” — envy at someone else's good eye is itself the evil eye at work.
Closing
A lamp does not manufacture its own light — it only lets light through, or blocks it. Jesus says the eye works the same way for the whole person. Fixed on treasure in heaven, open-handed toward the need in front of it, undivided in its aim — the eye lets in light, and the whole body follows it. Fixed on what it can keep, the eye goes dark, and calls its own darkness sight.