Augustine of Hippo

If "God be light, and in Him is no darkness at all, and we must have fellowship with Him," then from us also must the darkness be driven away, that there may be light created in us, for darkness cannot have fellowship with light. "If we say that we have fellowship with Him, and walk in darkness, we lie." Thou sayest thou hast fellowship with God, and thou walkest in darkness; "and God is light, and in Him is no darkness at all:" then how should there be fellowship between light and darkness? At this point therefore a man may say to himself, What shall I do? how shall I be light? I live in sins and iniquities. There steals upon him, as it were, a desperation and sadness. There is no salvation save in the fellowship of God. "God is light, and in Him is no darkness at all." But sins are darkness, as the Apostle saith of the devil and his angels, that they are "rulers of this darkness." He would not call them of darkness, save as rulers of sins, having lordship over the wicked.