See it is right there. We must cleanse ourselves. So the idea is when you blow it or are still struggling with addictions and bad habits you are perceived to be filthy and dirty before God.
...perfecting holiness in the fear of God. 2 Corinthians 7:1
You're not only dirty but now must perfect your holiness. So believers go about their lives and look to outward means to ensure they're perfecting holiness. Allow me to illustrate what this looks like in the average believers life.
Believer hears the good news. Gets saved. Realizes they're in right standing by what Jesus did. Now the preacher says they need to focus on their holiness before the Lord. That is what is most important. Believer goes home and contemplates this news.
So believer begins by cutting his hair and covering those tattoos. Goes to church and hears that is insufficient. So, believer quits watching certain TV shows. Goes back to church and hears that is insufficient. So believer quits listening to hard rock but still listens to country music. Goes to church and hears that is not enough.
Believer can't understand so he quits wearing shorts and no longer wears jeans to church but a suit. Again at the church he hears that is not enough. Believer goes home and quits listening to all music but Christian music and turns off the TV. Goes to church and hears it's still not enough. He realizes it must be the nicotine addiction. He tries and tries to beat the habit. Each time he lights up he realizes how dirty and filthy he is to God. He weeps each time he finishes a cigarette. Finally, after so long he quits. Yet with all these things keeping his focus his wife feels neglected. His wife leaves and he finds himself divorced. The church then kicks him out because divorce is the unpardonable sin. Believer gives up because this Christian life is too hard...
This happens all to often. This is why religion and tradition and legalism is so wrong and destructive to the Church. Allow me to give the good news. Righteousness is what He did and holiness is what He made you! It is not something He expects of you, it is what He has made you!
Put on your new nature, created to be like God—truly righteous and holy. Ephesians 4:24
By this will of God, we have been sanctified through the offering of the body of Jesus Christ once and for all,
...For by one offering He has perfected forever those who are sanctified. Hebrews 10:10,14
Holiness is what He made us. It is part of our new nature. This beautiful passage Paul is talking about in 2 Corinthians is a simple truth. He isn't saying cleanse yourself from your sin or bad habits. For only the Blood of Jesus cleanses us from sin and wrong.