You think you understand those verses pretty well, so how do you interpret verse 6?
"If we say that we have fellowship with him, and walk in darkness, we lie, and do not the truth:"
Do you say that you have fellowship with God, in spite of sinning against Him?
1 John 1:9 - If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness.
1 John 2:1 - My little children, these things I write to you, so that you may not sin. And if anyone sins, we have an Advocate with the Father, Jesus Christ the righteous. If Christians were sinless, without fault or defect, flawless, 100% of the time, then those verses would be superfluous.
Do you say that you have fellowship with God, in spite of saying that you have no sin, (present tense) deceiving yourself and the truth is not in you? (1 John 1:8).
1 John 1:6 - If we
say that we have fellowship with Him, and
walk in darkness, we
lie and
do not practice the truth. But if we walk in the light as He is in the light, we have fellowship with one another, and the blood of Jesus Christ His Son cleanses us from all sin. Walking in darkness is descriptive of children of the devil. Walking in the light is descriptive of children of God. Only those who are saved/believers are in the light.
Acts 26:18 - to open their eyes, in order to
turn them from darkness to light, and from the power of Satan to God, that they may receive forgiveness of sins and an inheritance among those who are sanctified by faith in Me.
2 Corinthians 6:14 - Do not be unequally yoked together with unbelievers. For what fellowship has righteousness with lawlessness? And
what communion has light with darkness?
Ephesians 5:8 - for you were
formerly darkness, but now you are Light in the Lord; walk as children of Light. Children of the devil walk in darkness, not in the light. Children of God walk in the light, not in darkness. IF confirms these positions in verses 6 and 7. It's one or the other.
In 1 John 2:9, we read - He who
says he is in the light, and
hates his brother, is
in darkness until now. In vs. 11 - But he who
hates his brother is
in darkness and
walks in darkness, and does not know where he is going, because the darkness has blinded his eyes.
*Compare with 1 John 3:10 - In this the
children of God and the children of the devil are manifest: Whoever
does not practice righteousness is not of God, (compare with 1 John 1:6 -
does not practice the truth) nor is he who
does not love his brother. *Notice that "walks in darkness, hates his brother" is in reference to children of the devil.