Luke 11:34-35 “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. Take heed therefore that the light which is in thee be not darkness.

The thing that brings light, illumination, or understanding to the body or the mind is the eye; which can be the physical eyes or the eyes of the mind. Our eyes, whether they are our physical eyes or the eyes of our mind, bring understanding to what is before us.  But that understanding can be darkness, or rather that understanding can be evil.  And when our understanding or our light is evil, we remain in darkness.  When the thing that brings light or ...