Luke 11:35
ESV - 35 Therefore be careful lest the light in you be darkness.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
Lk. 11:34 says, "The light of the body is the eye: therefore when thine eye is single, thy whole body also is full of light; but when thine eye is evil, thy body also is full of darkness"
The eye is the lamp that gives light to the body (Mt. 6:22).
Greek: haplous (G573) is used to refer simple, single, whole, good, and sound. Used only here and in Mt. 6:22 and only in the moral sense.
If the eye is single and sound morally and free from any lusts the whole body will be free from sin and morally sound and perfect. Light and darkness are used to contrast spiritual knowledge and spiritual blindness, and righteousness and sin (Mt. 4:16; Lk. 1:79; Jn. 1:5; 3:19; 8:12; 12:35,46; 1Jn. 1:5-7; 2:8-11).
If the eyes are full of adultery and lusts the body will be dark and the life blind (2Pet. 1:9; 2:14; 1Jn. 2:15-17 Rev. 3:17-18).