Luke 11:16
The lamp of the body teaching connects the outward reception of light to the inward condition of the eye — the eye is the body's lamp, and when it is healthy (single, generous) the whole body is full of light, but when it is bad (envious, stingy) the whole body is full of darkness. The warning is against the darkness within that appears as light: if the light in you is darkness, how great is that darkness (Matthew 6:23, Proverbs 20:27).