Logion 24

24. His disciples said unto him, “Show us the place where thou art, since it is needful for us to seek unto it.”
He said to them, "Whosoever hath ears, let him hear. There is light within a man of light, and he lighteth the whole world. If he shineth not, he is darkness."
Mt 6:22,23: The light of the body is the eye: if therefore thine eye be single, thy whole body shall be full of light. But if thine eye be evil, thy whole body shall be full of darkness. If therefore the light that is in thee be darkness, how great is that darkness.
Lk 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. If thy whole body therefore be full of light, having no part dark, the whole shall be full of light, as when the bright shining of a candle doth give thee light.

On the surface this seems to be a very simple principle. Both Mathew and Luke have thought to enlarge upon it. It is quite likely that any additional enlargement will be counter-productive. The simple principle seems to relate to the potentially great influence on the world that a simple human deed can have. Jesus and few others have stood in a place or had such light that their words and deeds have taken on such permanence and durability.