God Is Light

1 John 1:5
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.
There are five "ifs" in this text, one for each verse and all predicated on verse 5. God is light and in him there is no darkness at all. Because of that

First, if we say we have fellowship with God but walk in darkness we lie.
It appears that the sin is not the darkness as much as saying we have fellowship with God while we are walking in darkness.

Second, if we walk in the light as He is in the light we have fellowship one with another.
The condition is "as He is in the light" and the reward is fellowship. I take it from the context that is with God.

Third, if we say we have no sin we deceive ourselves.
Saying we have no sin is walking in darkness. It is ignoring the truth about ourselves. Walking in light is being honest with ourselves.

Fourth, if we confess our sins He is faithful and just.
Honesty before our own selves AND before the Lord.

Fifth, if we say we have not sinned we make Him a liar.
We have progressed to the point that we are imputing the darkness to God. The word is not in us because the Word plainly tells us we have sinned