But grow in the grace and knowledge of our Lord and Savior Jesus Christ. To him be the glory both now and forever. Amen. 2 Peter 3:18
The only sin that can't be forgiven is unconfessed sin?
Allow me to bring up another verse.
We don't confess our sins to be forgiven. Also, understand continually confessing our misdeeds and faults creates a failure mentality. Grace teaches us that when we acknowledge all we have in Christ we grow and experience victory. However, there is a principal of confession to find healing and recovery, (James 5).
This is an Old Covenant statement however, there is a truth we can extrapolate from it. We shouldn't conceal our wrongs. The enemy loves darkness. When you are struggling with a habit or sin it is so freeing to find a trusted brother or sister in the Lord and confess this issue. To get it out in the light and see the darkness flee and lose its hold upon you. This is the confession of sin for the New Covenant believer. We allow the light to expose and heal our hearts. Let me say it another way.
When the Spirit convicts us of our righteousness when we miss it, He is showing us who we already are, our true identity. This is when true repentance occurs. We change our minds about our actions. We confess or say the same thing as God does. We simply agree with God. We agree this action isn't profitable and not who we really are. That is all confession is for the believer. It is agreeing with God. We don't confess our sin to be forgiven. We are already forgiven. This is the good news. Rest knowing you are freely and completely forgiven.