"This then is the message which we have heard of him, and declare unto you, that God is light, and in him is no darkness at all." (1 John 1:5)
God is Love, and God is Light.
Because He is Light, He is perfect Justice, and cannot overlook sin.
When Jesus, the Light of the World (John 8: 12) died on the Cross, He shed His blood, which established a New Covenant in which God the Father would remember our sins no more (Hebrews 8: 12)
Because God is Light, and because all our sins have been punished forever in the body of His Son, we can now walk in His light, and never worry about our sins being exposed:
"But if we walk in the light, as he is in the light, we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin." (1 John 1: 7)
When we walk in God's Light, by the way, we do not merely see that we are not longer dirty, but we learn to see more of Him:
"For with thee is the fountain of life: in thy light shall we see light." (Psalm 36: 9)
The Psalmist connects God's Light and His Life.
How could it be otherwise?
"Then spake Jesus again unto them, saying, I am the light of the world: he that followeth me shall not walk in darkness, but shall have the light of life." (John 8: 12)
But how do I walk with Him?
It's even easier than that!
"Giving thanks unto the Father, which hath made us meet to be partakers of the inheritance of the saints in light:" (Colossians 1: 12)
You are in the Kingdom of Light because you believed on Jesus!
"To whom God would make known what is the riches of the glory of this mystery among the Gentiles; which is Christ in you, the hope of glory:" (Colossians 1: 27)
The Light of the World now lives in you!
"For ye were sometimes darkness, but now are ye light in the Lord: walk as children of light:" (Ephesians 5: 8)
Because God is Light, and His Son is your light, and you are a child of light through His Son!