Or don’t you know that all of us who were baptized into Christ Jesus were baptized into his death? (Romans 6:3, NIV)
Verse 3 makes it clear that we enter into the life of Christ at the point of his death. Knowing that is the foundation of our life in him. Our life is a life of resurrection.
Paul says it again: For we know that our old self was crucified with him so that the body of sin might be done away with, that we should no longer be slaves to sin. (Roman 6:6, NIV) It may take a long time to rid ourselves of the habits and evidence of sin, but by God's decree it has been accomplished in the spiritual realm.
In verse 9 Paul emphasizes that as Jesus lives by the Spirit, we also follow him in a spiritual life. Death no longer has any dominion over him. We will indeed die in the body, but the Spirit has already secured us in Christ for eternal life. We KNOW these things, and our faith rests of knowing his truth.