The new man in Christ does not have a sinful nature. When you received Christ, you were also circumcised by putting away your sinful nature. Human hands didn’t circumcise you. Christ did. – Col.2:11. It’s possible in a moment of weakness to fall back to Romans 7 and live as though we still have a sin nature, but we can decide to live in Romans 8 because we don’t really have one.
I disagree with this interpretation. The first word in Romans 8:1 (therefore) indicates it refers back to Romans 7:14-25 and is meant to be its conclusion. In effect Paul was saying that because of his sin nature he couldn’t prevent himself from sinning. But from God’s perspective it wasn’t Paul who sinned but the sin nature that lived within him (Romans 7:20). Therefore there is now no condemnation for those who are in Christ Jesus.
Having already forgiven all the sins of our life at the cross, God no longer counts them against us (Colossians 2:13-14). Otherwise, since our salvation is guaranteed from the moment we believe (Ephesians 1:13-14), Jesus would have to be crucified all over again each time we sin. But because of His once for all time sacrifice, we have been made perfect forever (Hebrews 10:12-14) in God’s sight.
Also in 1 Cor. 15:53 Paul said we will be changed from mortal to immortal at the time of the rapture. It’s our sin nature that makes us mortal, and it will be with us until the time of the rapture.