blepō

This is the everyday, physical meaning of the word: light reaches the eye and a person sees. It covers both having working eyes, as opposed to being blind, and the plain act of looking at a particular thing.

Greek did not build all its words for seeing out of one root. Several words shared the work, and this one supplied the ordinary present form, "I see" or "I am looking," while other words carried "I saw" and "I will see." The other main verb for seeing (ὁράω) had largely lost its present form in everyday speech, and this word stepped into the gap. That is a fact about how the language was put together, not evidence that this word means a shallower kind of seeing than its relatives.

Because it pictures sight in progress, it often has the feel of watching rather than of one quick glance. The Gospels use it constantly in stories about blindness and healing, where the question is literally whether a person can see. It is also the plain word for a witness watching something happen, such as the disciples staring upward as Jesus is taken from them, or John reporting what passes before his eyes.

Aimed at a listener as a command, the word shifts from plain sight to a charge: keep your eyes open. English Bibles render it "watch out," "beware," "take heed," or "see to it."

Two things can be in view. Usually it is a threat, and the threat is named: false teachers, hypocrisy, division, pride that comes before a fall, a heart drifting away from God. Sometimes it is a responsibility instead, and the charge is to pay close attention to how you are doing something, or to make sure a thing actually gets done.

This is not special religious vocabulary. Ordinary letters written on scraps of papyrus in the same century use the same word the same way, telling a friend to watch out for someone or to see that he forgets nothing. So these warnings are everyday speech, not a phrase coined by the early church.

Sight is a natural picture for understanding, and this word crosses easily from the eye to the mind. It can mean to notice, to recognize, to take in a fact, or to come to understand what something means.

The sharpest use plays the eye against the mind: people look straight at something with working eyes and still fail to grasp it. Jesus applies the words of Isaiah to crowds who watch his works without perceiving them, and Paul sets what can be seen against what cannot, so that faith reaches toward what the eyes cannot reach.

One fixed turn of phrase pushes the same idea in a different direction. To "look at the face" of someone is to be swayed by their standing, which is why the men who came to trap Jesus over the tax opened by granting that he does not size people up that way.

The line between watching with the eyes and grasping with the mind is often deliberately thin, and the writers cross it inside a single sentence to make their point. Which side of the line a given verse falls on is decided by reading that sentence, not by the word itself.

Once the word is used the way we say that a window or a harbor looks toward a direction. It describes the lay of a place, and nobody is seeing anything.

This is ordinary Greek rather than a stretch. Writers long before the New Testament described houses as facing south in just this way, and the Hebrew word for turning to face a direction (פנה) stands behind the same use in the Greek Old Testament. The New Testament happens to use it once, of a harbor on Crete open toward the southwest and northwest.