The lamp of the body is the eye: therefore when your eye is sound, your whole body also is full of light; but when your eye is evil, your body also is full of darkness.
All Commentaries on Luke 11:34 Go To Luke 11
Cornelius a Lapide
AD 1637
The light of the body is the eye. Figuratively the eye represents reason, intellect, especially good intention—for what the eye is to the body, such is reason or good intention to the mind.
When thine eye is single, thy whole body also is full of light, i.e. illumined by a single, a clear and unclouded eye.