Mat 6:22 The light of the body is the eye: if therefore thine eye be single, thy whole body shall be full of light.
The lamp of the body is the eye. If, in fact, it might be, that eye of yours, focused, the entire body of yours, shining, it is going to be.
There are several hidden plays on words in this verse, more if we consider it together with the following verse, Mat 6:23. This verse makes more sense in the context of Christ view of "light" and its connection to "truth" and "virtue". For more on the words used to mean "light" refer to this article.
The word translated as "light" means a portable light, a lamp. Christ uses "light" as a metaphor for knowledge and awareness, specifically that which allows use to perceive information.
The words translated as "of the body" means "the body" but it also means "the substance of things" generally, as we use the term "a body of evidence." So generally, it refers to material existence. Christ uses another Greek word to refer more specifically to his physical body or "flesh".
The Greek word translated as "is" is the active, present form of "to be."
The Greek word for "eye" is the more technical terms for "eye" but it also means "sight". It is a metaphor for "cheer."
The "if" phrase here is the form that indicates something that will probably happen, but not something that always happens or is just possible.
The Greek word translated "therefore" either emphasizes the truth of something ("certainly", "really") or it simply continues an existing narrative. "therefore" and "then". Either works here.
The Greek word translated as "be" here is in a form indicating something that "might be." In English, this form is assumed with the "if" that begins the phrase.
The Greek word translated as "single" means "single" which makes the KJV closer to the Greek than many more modern translated that render this word as "good". The adjective form means anything from "straightforward" to "simple-minded". In this context, the sense is the English phrase "single-minded" or, better, "focused." Double vision is a defect of the eye, a lack of focus. Single-vision good, double bad.
The word translated as "whole" means "complete" and "entire," but it also has a number of other meanings including "the universe" and "speaking generally."
The first time the Greek word for "body" was used, it was generic. Here, it is specific, "your body" so the sense it gives is of an individual's physical life.
The Greek word translated as "shall be" is the future tense of the common form of "to be." It appears at the end of the sentence.
There are not Greek words here that can be translated as "full of" except as an explanation of the following word.
The Greek word translated as "full of light" means "shining" and "bright." It has no sense of "full of", which is added to create a meaning not in the original. Since Christ uses light as a metaphor for knowing, the term "bright" works well because in English it means "intelligent." However, there is also a sense of "successful" and "well-known," as we might say that someone has a "bright career" or is a "bright star" in their profession. The final play on words is its use as a metaphor for seeing things clearly and distinctly, which makes perfect sense when talking about the eye or sight. For more on the words used to mean "light" refer to this article.
The triple meaning of being "bright" as in intelligent and "well-known" and the eye seeing things clearly and distinctly.
The Spoken Version:
“But my eyes can only see what is on the earth,” a wealthy man protested.
Many voices from the crowd agreed.
The speaker responded seriously. “The lamp of the body is the eye,” he explained. “If, then, it is—that eye of yours? In focus. That whole body of yours?”
As he said this, or perhaps right before, the clouds parted and a ray of bright sunlight fell upon the questioner.
“Shining!” The speaker declared. “It is going to be!”
ἐὰν (conj) "If" is from ean, which is a conditional particle (derived from ei (if)and an (might)) which makes reference to a time and experience in the future that introduces but does not determine an event.
ἁπλοῦς , (adj sg masc nom) "Single" is from haplous, which, as an adjective, it means "twofold", "single", "simple", "plain", "straightforward", "simple", "open", "frank", "simple-minded", "unalloyed[metals]," and "pure[metal].
ὅλον (adj sg neut nom )"Whole" is from holos, which means "the whole", "entire", "complete", "complete in all its parts", "wholly", "altogether", "on the whole", "speaking generally", "utter," "actually", "really, "the universe," and "safe and sound."