ophthalmos

This is the plain, bodily meaning of the word, the eye a person sees with. Almost everything else the word does in the New Testament grows out of this picture.

It shows up most often in the Gospels around sight and blindness: Jesus touches or anoints eyes and the blind see, and the eye stands for the whole act of looking and being seen. The same physical eye lies behind vivid figures of speech like a speck in your eye, plucking out the eye that trips you up, and an eye for an eye, where the word still names the literal organ even though the saying makes a larger point.

The New Testament repeatedly treats the eye as the way truth gets in, so that seeing and grasping run together. To have eyes opened is to finally understand; to have eyes that do not see is to be shut against what is plainly there.

Paul makes this explicit when he prays that the eyes of the heart would be flooded with light, an inward organ of perception rather than the bodily one. The same figure runs the other way in the hardening passages, where eyes are dulled or blinded so that people look without understanding, often echoing the language of Isaiah. The point in each case is not what the body can see but whether a person perceives and receives.

In a cluster of sayings the eye reveals the moral state of the whole person. A sound or single eye lets light fill the body, while a bad eye leaves it in darkness, a picture of generosity and integrity set against greed and divided loyalty.

This trades on an idiom common in the Jewish world of the time, where a good eye meant a generous spirit and an evil eye meant a stingy, grudging, or envious one. So when the vineyard owner asks whether his hearer's eye is evil because he is generous, the eye stands for begrudging envy, and the list of defilements that come from within includes the evil eye alongside greed and pride.