If we confess the sin [in] us, He is faithful and just to forgive us [our] sins, and shall cleanse us from all unrighteousness. If we say that we have not sinned, we make Him a liar and His Word is not in us.1 John 1:9-10
Denying the presence of sin isn’t how a believer addresses their sin. John has established a distinction between what it means “to have sin” (ἁμαρτίαν ἔχειν) in 1 Jn. 1:8, and “to sin” (αμαρτανειν).1 In other words, there’s both a sinful nature and sinful actions which are the fruit of that nature. Both are dealt with by confessing to the One who is faithful and just.
Verses 8 and 10 echo each other. Saying you don’t have sin is self-delusion, and proof that the truth isn’t dwelling in you (v8); saying that you have not sinned makes God (who is the truth) out to be a liar, and demonstrates that His Word doesn’t dwell in you (v10). Refusing to acknowledge the sin nature and the sins themselves are not only the project of self-delusion, but it is also a slander against God’s Word.
Sandwiched between these statements regarding the false ways of addressing our sin is the simple explanation for how the Christian deals with both the sinful root and the sinful fruit. We confess the sin in us, and God forgives our sins. The root is confessed, and not only is the fruit forgiven, but our unrighteousness is cleansed. Confession here is ὁμολογῶμεν (homologomen), which simply means to say the same thing as another. Of course, in this context we are agreeing with what God says about our sinful condition and our sinful actions. The conditional promise here is that if we confess our sin He not only forgives our sins, but he reckons us as righteous. He not only passes over our sin, but declares that we are not guilty.
This promise is one of the most golden passages of Scripture. In this simple promise the Gospel is held forth in all its profound glory. Sinners who confess their sinfulness, find in God a God who maintains His standard of justice, and yet forgives sinners because their unrighteousness is cleansed by the covering of another (1 Jn. 2:1-2).
1 Smith, David. The Expositors Greek Testament. Edited by W. Robertson Nicoll. Vol. Five. Grand Rapids, MI: Eerdmans, 1979. Pg 172