D&C 93

The Lord instructs us on what is known as the Light of Christ telling us that it is -

"...the light which shineth, which giveth you light, is through him who enlighteneth your eyes, which is the same light that quickeneth your understandings;
12 Which light proceedeth forth from the presence of God to fill the immensity of space—" (Doctrine and Covenants | Section 88:11 - 12)

But to actually receive the Light of Christ within us, we have to be worthy. Holiness has a lot to do with the level of reception. Our spiritual selves must be working properly to receive the Light for -

"...here is the agency of man, and here is the condemnation of man; because that which was from the beginning is plainly manifest unto them, and they receive not the light.
32 And every man whose spirit receiveth not the light is under condemnation." (Doctrine and Covenants | Section 93:31 - 32)

For -

"...the Spirit giveth light to every man that cometh into the world; and the Spirit enlighteneth every man through the world, that hearkeneth to the voice of the Spirit." (Doctrine and Covenants | Section 84:46)

When there is no light, there is darkness. They cannot co-exist. And -

"He that keepeth his commandments receiveth truth and light, until he is glorified in truth and knoweth all things." (Doctrine and Covenants | Section 93:28)