I like this passage when I am struggling with existing/recurring sin in my life. I just read it today, for much the same reason.
1 John 1:8-10 "If we say that we have no sin, we are deceiving ourselves and the truth is not in us. If we confess our sins, He is faithful and righteous to forgive us our sins and to 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."
So what this tells me is that anyone who says they don't sin is a Liar, and that they are deceiving themselves, and the truth and His word is not in them. Let us assume that most of our sin as Bible reading christians is in fact, on purpose. That is, we know what is wrong and we do it.
Romas 7:19 "For the good that I want, I do not do, but I practice the very evil that I do not want."
So, this tells me that there are sins in my life that I know are wrong and I did anyways, and that God knows my unrighteousness and will forgive me.
Often these sins are the same ones over and over.
But to me, as I look back, I see that I have struggled with a sin for a season and turned to Him to help and heal me and forgive sanctify me, and the sin occurred less and less. Cussing for example. Used to be a huge problem. Now the Holy Spirit convicts me before I even speak.
I think that unrepentance, the total and absolute REFUSAL to stop a sin when we know better and not turning to God for strength and forgiveness in the hope that we will do better, is the only thing we need to really worry about.
But for believers, let us not forget what Jesus told his disciples the MODEL for forgiveness really is, a model He surely applies to us. I make the assumption that a believer in Christ would not be OK with sin in his life to the extent that he would not do what he could to stop it even if it takes him awhile.
Matthew 18:21-22 "Then Peter came and said to Him, 'Lord, how often shall my brother sin against me and I forgive him? Up to seven times?' Jesus said to him, 'I do not say to you, up to seven times, but up to seventy times seven.'"