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 cleanseth us. Literally this could read “keeps on cleansing us from all sin.” The blood of Christ was not like that of other men, for it was “the precious blood…without blemish and without spot” (I Peter 1:19), uncontaminated either by inherited genetic mutations or inherent sin. Somehow, after it was all poured out at the foot of the cross (John 19:34) in atonement for our sins (Hebrews 9:22-28), “by His own blood [Christ] entered in once into the holy place, having obtained eternal redemption for us” (Hebrews 9:12).

1:7 all sin. All sin, whether known or unknown, is cleansed by His blood, as we walk in fellowship with Him.