"Therefore there is now no condemnation for those who are in Christ Jesus" (Ro.8:1). The reason we are not under condemnation is simply that we are in Christ Jesus. The words "who walk not after the flesh, but after the Spirit" which follow this verse in the KJV were not really there in the original manuscript. This makes a lot of difference to us if we were imagining that only if our practical life was perfect could we have freedom from condemnation. No. We cannot live a perfect life on earth ever, and if we were waiting for perfection before we could be free from condemnation we would be feeling permanently guilty. But no. When we come to God trusting in the sacrifice Jesus made for our sins, our guilt is taken away and God justifies us before Him (4:5).
"Therefore ... no condemnation." There were no verses or chapters in the original text, and this artificial start of Chapter 8 tends to make us discard the previous chapters and treat this one as a standalone treatise on the life in the Spirit! The immediate verse before this says, "Thanks be to God through Jesus Christ our Lord! So then, on the one hand I myself with my mind am serving the law of God, but on the other, with my flesh the law of sin" (7:25). What! Paul is thanking God even while admitting a duality in his life � serving the law of God in his mind while serving the law of sin in his flesh! Isn't it wrong to disconnect this, pretend we don't have a flesh any more, and treat Chapter 8 as if chapters 6 and 7 are not relevant any more to believers?
Some may have a tendency to hold doctrine far above life and pretend as if there is no connection between the two � saying we are now in the Spirit according to Chapter 8! But let's be honest. We are tempted daily by the flesh (Jas.1:14) which is sometimes influenced by the world or the devil, and we may fall. In our mind and heart we do not want to fall (that is how we serve the law of the Spirit of life), but sometimes we discover we have done what we shouldn't have. That's our flesh serving the law of sin. We may not be always aware this is happening when we fall and realise only later what we have done. But when we realise it, we can ask for forgiveness. If we are humble enough to recognise this possibility and stand honestly before God, the Spirit can show us what happened and help us to do better next time.
But the fact of the matter is that even when 'we serve the law of sin in our flesh' there is no condemnation from God! He knows that we didn't mean to, and that we are serving the law of the Spirit in our heart and mind. He knows that as long as we live with this flesh we are not going to be able to fully follow the Spirit in everything and at all times. Therefore He takes away our condemnation even though that is what we deserve technically.
Of course, this doesn't mean we can indulge the flesh as we wish because that would not be walking according to the law of the Spirit in our heart and mind!