The eye is the light of the body and the window to the soul. If our eye is single (and Joseph Smith later added to the phrase “single to the glory of God”; Matthew 6:22, footnote b, from JST, Matthew 6:22; see also D&C 4:5), that is, if we are dedicated to our Savior’s glorious cause, then our whole body will be full of light (D&C 88:67). He is our light, so our whole life can be filled with his influence, and no darkness will persist in us. There is no life without Light.