1:7 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.
What it is to "walk in the light" is explained by 1 John 1:8-10 . "All things. . .are made manifest by the light" Ephesians 5:13 The presence of God brings the consciousness of sin in the nature 1 John 1:8 and sins in the life 1 John 1:9 1 John 1:10 . The blood of Christ is the divine provision for both. To walk in the light is to live in fellowship with the Father and the Son. Sin interrupts, but confession restores that fellowship. Immediate confession keeps the fellowship unbroken.
light (See Scofield "Exodus 27:20")