Paul struggled with sin terribley and realized that the sin nature would always be with him as long as he lived in the body of death we all live in as man that is our temporary tent or tabernacle. Our permanent bodies are compared to mansions that Jesus said He went to prepare. They will not have any sin or death associated to them to influence the soul to sin - making demands of it as the flesh does so often. See verses, all in New Living Translation:
Romans 7:15 - 8:1 I don’t understand myself at all, for I really want to do what is right, but I don’t do it. Instead, I do the very thing I hate. I know perfectly well that what I am doing is wrong, and my bad conscience shows that I agree that the law is good. But I can’t help myself, because it is sin inside me that makes me do these evil things. I know I am rotten through and through so far as my old sinful nature is concerned. No matter which way I turn, I can’t make myself do right. I want to, but I can’t. When I want to do good, I don’t. And when I try not to do wrong, I do it anyway. But if I am doing what I don’t want to do, I am not really the one doing it; the sin within me is doing it. It seems to be a fact of life that when I want to do what is right, I inevitably do what is wrong. I love God’s law with all my heart. But there is another law at work within me that is at war with my mind. This law wins the fight and makes me a slave to the sin that is still within me. Oh, what a miserable person I am! Who will free me from this life that is dominated by sin? Thank God! The answer is in Jesus Christ our Lord. So you see how it is: In my mind I really want to obey God’s law, but because of my sinful nature I am a slave to sin.
So now there is no condemnation for those who belong to Christ Jesus.
Galatians 5:16 So I advise you to live according to your new life in the Holy Spirit. Then you won’t be doing what your sinful nature craves.
17 The old sinful nature loves to do evil, which is just opposite from what the Holy Spirit wants. And the Spirit gives us desires that are opposite from what the sinful nature desires. These two forces are constantly fighting each other, and your choices are never free from this conflict.
As the others have advised, repentance is a process of battle against the flesh of sin and death and the evil that results of its wickedness, working upon the mind and soul of man. We fight the good fight of faith against that side of ourselves in battle and never just lie down in our sins, making repentance only a ritual or game we play that may eventually regard the blood of Jesus and His work at the cross lightly. Sometimes we have a great day of victory and sometimes we feel like Paul and confess how rotten we are in the old nature when it wins out. Either way, we must never give up our faith in God, but contend for it vigorously.
Let me add that we could never overcome sin and death without the blood of the lamb, and our testimony is that we have fought the good fight of faith against sin and death with God's help.
1Ti 6:12 Fight the good fight for what we believe. Hold tightly to the eternal life that God has given you, which you have confessed so well before many witnesses.
We know that God sees all things but is quick and merciful to forgive seven times seven and more....
Ga 6:7 Don’t be misled. Remember that you can’t ignore God and get away with it. You will always reap what you sow!