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John has in mind unbelievers who see themselves as sinless. This is an impossibility this side of glory. If they had truly been in the "light," the light would continually expose their sinfulness!

The Holy Spirit is constantly revealing our sin and God's holiness to us. We continue to grow in the grace and knowledge of our Lord and Savior Jesus Christ (2 Pet 3:18).

An example may help: As one gets closer and closer to a bright light, the more things are exposed. For instance, as more light is added to a room, dust that was on the dinning room table all along becomes more visible and prominent. Items that could not be seen before come into sharper focus. In a similar way, the closer we get to Christ (who is light - John 1:8-9; 8:12; 1 John 1:5), the more we discover that we are far greater sinners than we had ever thought. The closer our relationship with God, the more our sin will be in the light. This will cause the true Christian grief and result in repentance (2 Cor 7:10). True Christians live lives of ongoing repentance (2 Tim 2:24-26). Is this not different from how we were before Christ? Is this not evidence of our election?

Persons who think they no longer sin no longer have a need to preach the Gospel to themselves. This is evidence of their condition; they are lost. These false professors of light deceive themselves and remain in darkness. The Greek suggests an active rejection of the truth rather than simple misconception: "The truth is not in [them]." Thus they are not saved (cf. 1 John 2:4; 5:6). In denying their sins they also deny their need for the forgiveness found in Christ and thus reject the truth of the gospel. See WCF 6.5; 11.5; WLC 77, 149; WSC 82; BC 34; HC 1, 5, 30, 56, 72, 114.

Jackman conveys an interesting story:

Let us leave this issue with an incident recounted about Charles Haddon Spurgeon, the great Baptist preacher of the last century. Perhaps few other Christians in heaven will have such a long queue of preachers apologizing for having told so many apocryphal stories about them! Be that as it may, it is said that Spurgeon was once confronted by a man who claimed to be "without sin." Intrigued, the preacher invited him home to dinner. After hearing the claims through, he picked up his glass of water and threw it in the man's face. Understandably, the visitor was highly indignant and expressed himself very forcefully to the preacher about his lack of courtesy. To which the wise man replied, "Ah, you see, the old man within you is not dead. He had simply fainted and could be revived with a glass of water!"

without sin. This phrase only shows up here in First John, but is used four times in the Fourth Gospel (see notes on Jn. 9:41; 15:22, 24; 19:11). This is the first false claim from those who have left the church. They seem to be claiming a heightened spiritual state in which they have ceased from sinning. deceive… truth. The Greek form of the word deceive is emphatic, talking about an active rejection of the truth. To say "I have no sin" or "I am sinless" denies the reality of sin. The Bible consistently teaches that everyone is guilty of sin (see notes on 1 Kgs. 8:46; Pss. 14; 143:2; Eccl. 7:20; Mk. 10:18; Rom. 3:9-26). Truth can describe God himself, or Jesus (see note on Jn. 14:6). So, this is saying that the people who claim to have stopped sinning are not Christians, that God is not in them (see notes on 2:4; 5:6).

When one is enabled to place their trust in Christ, they are justified and forgiven in the court of heaven itself (Rom. 5:1; 1 John 2:12). See "Justification and Merit: Why Does God Count Me as Righteous?" below. In this ultimate sense, the final destiny of true believers does not depend on their confessing sins day by day. Even so, we do not experience the full benefits of our justification this side of glory. As a result, true believers sin and therefore are in need of the experience of continual forgiveness from God (a gift - 2 Tim 2:24-26). They enjoy God's blessing rather than his temporary discipline (Heb. 12:5-11) when they readily acknowledge their sins before him. Therefore, as Stott says, "The proper Christian attitude to sin is not to deny it but to admit it, and then to receive the forgiveness which God has made possible and promises to us." See "The People Grieve - Ezra 10:1" below.

Repeated and unrelenting rebellion against God may indicate that a person does not have saving faith, but those who genuinely trust Christ for salvation will heed John's call for confession. See "Deliberately keep on sinning - Hebrews 10:26" below. See WCF 11.5; 15.6; HC 115.

God is faithful and just. This is the believer's full assurance. God is faithful with respect to all his promises (Deut. 32:4). He is the one who has the power to forgive and who does forgive his people their sins (Jer. 31:34; Heb. 8:12; 10:17). Even in the Old Testament we observe God's call to the Church to be forgiven: "Come now, let us reason together... Though your sins are like scarlet, they shall be as white as snow; though they are red as crimson, they shall be like wool" (Isa. 1:18). Stott also says:

If we confess our sins, acknowledging before God that we are sinners not only by nature (sin) but by practice also (our sins), God will both forgive us our sins and purify us from all unrighteousness. In the first phrase sin is a debt which he remits and in the second a stain which he removes. In both he is said to be faithful and just. The first word may mean that he is faithful to his nature and character (cf. 2 Tim. 2:13). But the faithfulness of God in Scripture is constantly associated with his covenant promises (e.g. Psa. 89; Heb. 10:23). He is true to his word and faithful to his covenant. Since the new covenant includes the pledge, I will forgive their wickedness and will remember their sins no more (Jer. 31:34), it is not difficult to see why God is said to be 'faithful' in forgiving our sins.

confess. See WCF 11.5; HC 115. When Christians confess their sins, a just God forgives them on the basis of Christ's faithfulness to the point of death for the sake of sinners. Here, John uses the plural "sins" (rather than "sin", like in v. 8). This could refer to the confession of specific sinful acts, instead of the general idea of "sin". The confession of sins is a characteristic practice of true disciples of Jesus

In 1 John 1:10, John is speaking of an explicit denial of having committed sinful acts (cf. 1 John 1:8). Kistemaker says that the statement "we have not sinned" reveals the blatant attitude of the unrepentant, unregenerate infidel. Those who deny their own sins are not saved (cf. 1 John 1:8; 2:14). Just as the truth is not in those who deny their sins (1 John 1:8), neither is God's word. These words warn against any claim that believers are able to live without sin in this life. As Calvin puts it, "Thus we learn that we only make due progress in the knowledge of the Word of the Lord when we become really humbled and groan under the burden of our sins and learn to flee to God's mercy and find rest in nothing except his fatherly favor." See WCF 6.5; 13.2; WLC 77, 149; WSC 82; HC 2, 5.

We are far greater sinners than we have ever imagined. In his sermon "Paul's Letter to the Galatians: Living in Line with the Truth of the Gospel," Tim Keller delineates this point:

The gospel of justifying faith means that while Christians are, in themselves still sinful and sinning, yet in Christ, in God's sight, they are accepted and righteous. So we can say that we are more wicked than we ever dared believe, but more loved and accepted in Christ than we ever dared hope - at the very same time. This creates a radical new dynamic for personal growth. It means that the more you see your own flaws and sins, the more precious, electrifying, and amazing God's grace appears to you. But on the other hand, the more aware you are of God's grace and acceptance in Christ, the more able you are to drop your denials and self-defenses and admit the true dimensions and character of your sin.

1:10 we have not sinned… liar. John's opponents may not have claimed that they had never sinned in their lives, but, that they had not sinned since coming to know God. It is also likely that they viewed their bodies and use of material goods as morally inconsequential. In either case, verse 8 says people who deny their sinfulness do not possess the truth. This text ties the truth of Scripture, God's Word, to God's character. To deny the truth of Scripture by claiming to be sinless is equivalent to saying, 'God is a liar.'