This is the message we have heard from him and proclaim to you, that God is light, and in him is no darkness at all.  If we say we have fellowship with him while we 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 his Son cleanses us from all sin.  If we say we have no sin, we deceive ourselves, and the truth is not in us.  If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness.  If we say we have not sinned, we make him a liar, and his word is not in us. 1 John 1:5-10 ESV
John wrote this letter to the recipients at a time when Gnosticism was spreading through the church. Gnosticism taught that matter was evil so we see John’s emphasis on His interaction w/Jesus through touch, sight, and sound. It also taught that salvation was acquired through a secret knowledge. However, we know that God makes Himself known through the preaching of the Gospel.
John’s desire was to proclaim the message of the Gospel so that the recipients would have fellowship with God and others and that their joy be complete. We have fellowship with God when we walk in obedience, and when we confess our sins.
Throughout the book of 1 John, we see a lot of statements that begin with “if”, starting with this passage. If we say “this”, then “that” should be true of our lives.
We have fellowship w/God when we walk in obedience. (v5-7)
 This is the message we have heard from him and proclaim to you, that God is light, and in him is no darkness at all.  If we say we have fellowship with him while we 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 his Son cleanses us from all sin.
John builds a foundation in verse 5 by pointing to God’s character – He is light and in Him is no darkness at all. By using the term light, John is referring to God’s holiness, His purity. He is without flaw, without shadow, without error. John continues to use this contrasting theme of light and darkness in the 2nd chapter of this epistle, and he also used it in the Gospel of John. Since God is light, those that profess to be His should be walking in light, reflecting His character, His goodness, His holiness. We should be holy as He is holy, as God instructed His people in Leviticus 11 & 19. Peter references this when he speaks in his epistle in 1 Peter 1:
 As obedient children, do not be conformed to the passions of your former ignorance,  but as he who called you is holy, you also be holy in all your conduct,  since it is written, “You shall be holy, for I am holy.” 1 Peter 1:14-16 ESV
If we say that we belong to God, our overall lives as Christians should be marked by walking in light. So what does it mean to walk in darkness? I believe Galatians 5 provides some good examples of this in verses 19-21: sexual immorality, impurity, sensuality, idolatry, sorcery, enmity, strife, jealousy, fits of anger, rivalries, dissensions, divisions, envy, drunkenness, orgies, and things like these. It goes on further to say at the end of verse 21 that those who do such things will not inherit the kingdom of God, showing that there is no true fellowship with Him. And if there is no true fellowship with God, there is no true fellowship with His people. So we are to walk in the light as He is in the light.
Now, as we all know, we often fail to walk this way. There are times when we walk in darkness and our fellowship with God & others experiences discord. What are we to do then? We confess our sins to our God. Let’s look at verses 8-10.
 If we say we have no sin, we deceive ourselves, and the truth is not in us.  If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness.  If we say we have not sinned, we make him a liar, and his word is not in us.
We see in verses 8 and 10 that our lack of confession is self deception and ultimately a declaration of God to be a liar. It is an assault on God’s very character. The truth of the matter is that we are all sinners. Romans 3:9 asserts that none of us are righteous while stating later on in verse 23 that we have all sinned and fallen short of the glory of God. Since we know the Bible is God’s Word, and we know that God’s Word is true, for us to say that we have not sinned, we deceive ourselves greatly and put ourselves in a place that calls for God’s discipline. David says in Psalm 32:
For when I kept silent, my bones wasted away
through my groaning all day long.
For day and night your hand was heavy upon me;
my strength was dried up as by the heat of summer. Selah
Psalm 32:3-4 ESV
Sin is destructive, and it destroys and hardens the heart of the unrepentant sinner. When our hearts are hardened, it makes it even more difficult to respond to God’s correction. Our willful sin also invites God’s discipline.
I can remember times at my previous place of my employment when I’d struggle with confessing my sins to God. In my failure to confess my sin when I’d failed to trust the Lord, or spoke to someone wrongly or responded wrongly, I found myself being my own defense attorney, seeking to justify myself. This just led to further destruction of sensitivity to God’s gracious conviction. I could feel the distance between myself and Him. When I would confess my sin to Him, there was such a sweet reconciliation that took place. To know that God loved me and forgave me encouraged my heart.
There is such great blessing when we confess our sins to God! Verse 9 tells us that He is faithful to forgive us and cleanse us of all unrighteousness! He does what we cannot do. He restores us back to relationship with Himself and others. James 5:16 says that when we confess our sins to one another, healing can occur. We experience reconciliation between ourselves and God and between ourselves and others. Oh friends, won’t we be quick to confess our sins to God so that we may know His great mercy and grace in forgiveness? May we also be quick to confess to others! I can say that in those times when I have been slow to confess my sin to my husband, there has been marital discord. If you are married, I am sure you understand the effects of failing to admit your sin to your spouse. Harmony is interrupted until confession occurs, and when it does occur, what sweet reconciliation takes place. Praise God for His grace to us!
So, believers in Jesus Christ, what must we do with this passage of Scripture?
First, we must walk in the light. Walk in a way that reflects the holy purity of God. Colossians 1:10 says to walk in a manner worthy of the Lord, fully pleasing to him, bearing fruit in every good work and increasing in the knowledge of God. The way that we walk is informed by His Word. As we consistently read God’s Word, we will increase in our knowledge of Him and His Spirit will sanctify us and conform us into the image of Jesus Christ.
Second, we must confess our sin and turn away from it, and in doing so, remember that our God is a God who will forgive you and cleanse you of all sin. Confession & repentance is an ongoing, daily thing. Pray for God to make you sensitive to the Holy Spirit’s conviction. Pray that your heart will be ever sensitive to sin. Pray that you would be slow to sin, but quick to confess. Pray that you would humble yourself and be transparent before God and before others.
You may say, what do I do if I am not a believer in Jesus? What if my life is one that is characterized by walking in darkness?
You have asked a great question. As I stated before, we’re all sinners. We are born at war against God. Our very nature goes against all that He is. There is nothing we can do on our own that would do away with this fact. And because God is light – He is holy, He is pure – He must punish sin. This is what we deserve. Our sin earns His wrath and eternal punishment. Because we cannot appease God’s wrath on our own, there had to be a sacrifice for our sin. Someone had to live a righteous life. That Someone is Jesus, God’s very own son whom He sent to live the life we should live, but die the death that every single one of us deserves to die. He was crucified on a cross, died, and rose, proving that He was not guilty and He was indeed the Son of God. Because He lived the perfect obedient life we should live, when we confess our sinfulness and place faith in Him, we receive His righteousness into our account because He received the punishment for our sin. My unbelieving friend, God’s Word says that He is faithful to forgive and cleanse of all unrighteousness upon confession of our sins. What will you confess? Will you confess your sins to God and receive His forgiveness, cleansing, and grace? Or will you reject Him and say that He is a liar?
Let us walk in the light, as He is in the light, confessing our sin to the God who is ever faithful to forgive.