John the apostle is good at drawing contrasts. In the first chapter of his first epistle, John has contrasted light with darkness, walking in light with walking in darkness, and lies with truth. Now, John is contrasting the consequence of not confessing our sins with the consequences of confessing our sins.
John makes the statement that if we do not confess our sins, we deceive ourselves. This is true! Human beings often try to justify their unjust actions in order to prevent the logical outcome of a confession to a holy God. Whenever we justify our actions, we are truly deceiving ourselves, and more than that. We are robbing ourselves of precious time with our Creator.
John also makes it clear that, when we justify our actions and deceive ourselves, the truth is not in us. When we justify our actions, we have become liars. This is a very bad place to be.
The contrast that John draws with this is one of confessing our sins. In order to confess our sins, we must first realize that we have sinned! We must also know Who to confess to! Once we have realized that we have sinned and know Who we can go to in order to confess our sins, we can come to Him and ask for forgiveness. However, there is more to this.
John makes it clear that, when we come to God and confess our sins, He is both faithful and righteous to forgive us of our sins. He is faithful to do this. He will not forget to forgive, or refuse a truly repentant heart. However, there is more to this.
God is not just faithful to forgive us for our sins. He is also faithful to cleanse us from all unrighteousness. Not just some. Not just in part. He will not only forgive us. He will help us get rid of the problem. This being the case, there is no reason we should not trust Him to do so.