Read 1 John 1:5-10
For a person to walk in the light requires that he first receive Christ as personal Saviour. The light of God's Word must first have enlightened that person's heart and convicted him of his sin.
That same light reveals to us the holiness of God and brings us to a reverential fear of Him, something foreign to the natural man (see Rom. 3:18).
That same light reveals to us how Christ came to reconcile us to God. To us is offered "the righteousness of God which is by faith of Jesus Christ unto all and upon all them that believe: for there is no difference" (Rom. 3:22).
Christians who walk in the light become increasingly conscious of the holiness of God and of the sinfulness of sin. They are not deluded into denying that they have a sinful nature.
They realize that they still have sinful tendencies that are expressed in fleshly impulses, nonspiritual inclinations and standards of living that are patterned after the world rather than after God.
These are all sinful in the sight of God, and to call them righteous rather than sinful is to walk in darkness. Should we even so much as waver in our trust in God, we sin, for the Word says, "Whatsoever is not of faith is sin" (Rom. 14:23).
"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).