“The eye is the lamp

Of the body.

So,

If your eye is clear,

Your whole body

Will be full of light.

But if your eye is

Evil,

Your whole body

Will be full of darkness.

If then the light

In you

Is darkness,

How great is that darkness!”

Ὁ λύχνος τοῦ σώματός ἐστιν ὁ ὀφθαλμός. ἐὰν οὖν ᾖ ὁ ὀφθαλμός σου ἁπλοῦς, ὅλον τὸ σῶμά σου φωτεινὸν ἔσται·

ἐὰν δὲ ὁ ὀφθαλμός σου πονηρὸς ᾖ, ὅλον τὸ σῶμά σου σκοτεινὸν ἔσται. εἰ οὖν τὸ φῶς τὸ ἐν σοὶ σκότος ἐστίν, τὸ σκότος πόσον.

This saying of Jesus is similar to what is in Luke, chapter 11:34-35, so that it may be from the Q source.  The eye was the lamp of the body (Ὁ λύχνος τοῦ σώματός ἐστιν ὁ ὀφθαλμός).  If there was a healthy clear sound eye (ἐὰν οὖν ᾖ ὁ ὀφθαλμός σου ἁπλοῦς), then you would have a whole body full of light (ὅλον τὸ σῶμά σου φωτεινὸν ἔσται).  This is the only time that the word “ἁπλοῦς” is used in the New Testament literature.  Both Luke and Matthew used it here, since it means simple, sound, clear, or perfect.  If, on the other hand, your eye was not healthy or evil (ἐὰν δὲ ὁ ὀφθαλμός σου πονηρὸς ᾖ), your whole body would be full of darkness (ὅλον τὸ σῶμά σου σκοτεινὸν ἔσται).  Notice that Matthew did not use the opposite of clear, but chose the more common word for evil, “πονηρὸς.”  Thus, you had an evil eye.  On the other hand, both Luke and Matthew used a word that appears only here, “σκοτεινὸν,” to talk about a full total darkness.  If the light that is in you is dark (εἰ οὖν τὸ φῶς τὸ ἐν σοὶ σκότος ἐστίν), that is a really great darkness (τὸ σκότος πόσον).  Light and darkness was a common theme among the early Christians.  Light was good, but darkness was evil.  The connection of light to the eye was natural since the sense of blindness and darkness centered around the eyes.