From what I understood here is that the new man who is a new creation in Christ does not sin in his spirit thats true as long as he is in an unbroken communion with God but if he gives in to the flesh he can pollute even his spirit, otherwise why would Paul exhort believers to be wholly sanctified spirit, soul and body if our spirit was already sinless or pure?
Everyone who holds that dualistic concept that spirit does not sin but its only in the flesh that we do sin, has to quote Romans 7 to support this teaching. Romans 7:14-25 in its context is applying to life under law and not under grace. Text out of context is a pretext and that's what many do with Romans 7 to support their dualistic view that is a relic of gnosticism and not apostolic teaching. If a Christian is dominated by the flesh he needs to be sanctified in the spirit as well as the body.
Paul makes it clear in Romans 8 that life dominated by the Spirit overcomes sin, if we are controlled by the Spirit we won't sin deliberately or knowingly, it is only when we give in to the flesh that we give in to temptation and sin and according to the bible we have the power to resist temptation and sin enters in when we give in to temptation.
We will have a mortal body for the rest of our lives because of the consequences of Adam sin but our body is the temple of the Holy Spirit and should be cleased from sin. The normal Christian life as described in the NT does not support this view that we should have sin in our body for the rest of our life? Our flesh if we live in the Spirit is not evil but mortal, its only sinful when we give in and live in sin and not in holiness. God meant life to be governed by the spirit and not the flesh, it is when we turn this order upside down that we are in big trouble. When we give in to the pleasures of the flesh we sin and when we let the Spirit control our life we bear fruit.
One who overcomes sin, the world, the flesh and the devil is called an overcomer in the Bible and slave of righteousness not slave of sin. Otherwise would be pointless for Paul to exhort believers and pray that they would be spotless and blameless in this life and not just in the one to come and a blameless life was one of the requirements for a bishop or an elder in the early church.
Also if Paul did not live a blameless life he would never said to believers to follow his example or imitate him as he imitates Christ, that would have made him a hypocrite.
The work and person of Jesus Christ has made it possible for a Christian to walk in an uninterrupted communion with God and not sin knowingly, if you believe this is sinlessless that's your choice, I see it at the normal Christian walk we are called into, to walk in the light as he is in the light and the blood of Jesus will cleanse us from all sin, it does not say only from actual sin and not from our sinful state, all means all.If you don't believe the blood of Jesus can cleanse us from all sin, you make sin more powerful than the blood that our Savior shed for us on the cross.
And I see this as accomplished only as we crucify the flesh and surrender to Jesus not only for a day as if that surrender was once for all at one moment in time but its actually a lifelong attitude of total surrender to Him. The only power to indwelling sin is the overcoming life of indwelling Christ within us. The secret is Christ in us, self has to be crucified daily, this is the only way to experience freedom from sin and that sanctification of heart that the Bible makes it a necessary requirement in the life of the believer.
Those that God has chosen he declares righteous in his sight because they believe his Son but the same Christians to whom he imputed righteousness of Christ in justification, he imparts the righteousness of Christ in sanctification by the same faith. There are two sides of the righteousness of God, one is the imputed righteousness and the imparted righteousness of Jesus. Those whom God declares righteous in his sight, are the same ones he makes righteous in Christ in the processs of sanctification.
Those who are genuinely regenerated and sanctified in the name of the Lord Jesus Christ and by the Holy Spirit are the true Christians who are justified in the sight of God. (See 1Corinthians 7:11)