We Christians are often far short of what Scripture says we should be. New Creations in Christ, People who have died to sin -- oh really?
I think there are three things we can do about this discrepancy.
1) Conclude that what Scripture says is wrong. I've started down this road many times, but by God's grace I haven't persisted.
2) Pretend that the discrepancy doesn't exist. Put on an act that we're good and OK and all is fine, and make our faith about something external rather than the state of our hearts.
3) Believe that Scripture is true, but that the promises are things to be claimed by faith and through God's grace in our lives. This is what Caleb and Joshua did about the discrepancy between the promises of God that Israel would be given the land of Canaan, and the reality they saw, that the land was inhabited by powerful enemies. And this is what Paul tells us to do in Romans 6. He says we have died to sin in Christ and have been raised with Him in a new life, but he then says we have to reckon or calculate ourselves to sin. It doesn't just happen automatically.