1:5 God is light. Since God is light, dwelling in light (I Timothy 6:16), He did not have to “create” light, but simply say: “Light, be!” (Genesis 1:3). On the other hand, He did create darkness (Isaiah 45:7) as the initial state of the unformed and uninhabited earth (Genesis 1:2). When light appeared to disperse the darkness, it could thereby become a model of the shining of spiritual light into a soul born in the darkness of innate sin (II Corinthians 4:6). Physically, God is the light of shining glory; intellectually, He is the light of truth; and morally He is the light of holiness. He is also the light of life (John 1:4) and of true guidance (John 8:12).
1:6 do not the truth. Note that the truth is not only something we should believe and teach, but also something we should do!
1:7 fellowship one with another. That is, we are in fellowship with the Lord, and therefore also with other believers who are in fellowship with Him. Since there is no darkness in God, if we truly walk in His light, there can be no reason for any error, sin, or ignorance of His will on our part.
1:7 all sin. All sin, whether known or unknown, is cleansed by His blood, as we walk in fellowship with Him.