1 John 1:5-10 ESV
This is the message we have heard from him and proclaim to you, that God is light, and in him is no darkness at all. If we say we have fellowship with him while we walk in darkness, we lie and do not practice the truth. But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus his Son cleanses us from all sin. If we say we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness. If we say we have not sinned, we make him a liar, and his word is not in us.
When God said "Let there be light", He was sharing Himself with creation. God is light. This light would come to be clothed in the flesh of man. Once the door to salvation was opened, the light of God continues to grow in the world and expand in the flesh of men. Darkness is left behind as believers come to the light.
Adam was expelled from the Garden and was clothed in animal skins by God. Jesus brings us back into the Garden and will clothe us in immortal bodies.
John tells us that the blood of Jesus cleanses us from all sin. This does not mean we no longer sin. It means that He has paid the price of sin once and for all. Forgiveness is ours if we confess our sins. If we ask, we receive. If we do not ask, we do not receive.
By confession, we wash our feet from the dirt of the world. The water of repentance and the blood of Jesus restore us to righteousness. This is walking in the light.