Charles Ellicott Commentary Matthew 6:22

"The lamp of the body is the eye: if therefore thine eye be single, thy whole body shall be full of light." — Matthew 6:22 (ASV)

The light of the body. This is literally the lamp of the body. So in Proverbs 20:27, it says, The spirit of man is the candle (or ‘lamp’) of the Lord—that which, under the name of “conscience,” the “moral sense,” or the “inner man,” discerns spiritual realities, distinguishes right from wrong, and gives the light by which we see our way.

If this lamp is “single,” meaning it discerns clearly, then all is well. The “whole body”—the person’s life in all its complex variety—will be illuminated by that light. The connection with what precedes this is clear: singleness of intention will preserve us from the snare of having a double treasure and, therefore, a divided heart.