Upon reading Romans 5–6, one sees that Jesus solved the problem that Adam created by reconciling us to God (Rom 5:10). Christ did this by dying for the ungodly (5:6), and it is implied that all humanity is somehow part of this group (Hurtado [Lord Jesus Christ, 133] notes that chapter 5 is the logical progression of Romans 3-4, in which we find the declaration that all of humanity is under sin [3:9-10]). When Adam sinned, sin found a doorway into the world and all have somehow partaken of sin (5:12). The result of sin is death, which all have experienced by virtue of having partaken of sin (5:14). In contrast, Jesus through his death brought life and grace to humanity (5:15-16). Moo notes that both Adam and Christ are “individuals whose actions affect all who belong to them” (“Christology of Early Pauline Letters,” in Contours of Christology, ed. Longenecker, 176).
We first participate in the new life offered in Christ by faith (5:1). Faith justifies a person, grants peace with God, and offers access to God’s grace and will result in sharing in God’s glory (5:1-2). The response of faith means the response of dying to sin and living in righteousness (6:2, 12-13). This death to sin comes from dying with Christ through baptism (6:3-5); As Hurtado points out, baptism was “widely practiced” among the early Christians (203). Living in righteousness is the result of the choice to live alive in Christ, specifically through the presentation of oneself to God (6:13).
I find it interesting that Romans speaks of unity with Christ as a reality in the present. In 6:5, the verb translated “have been united” conveys an action that has happened in the past with ongoing effects: the effect of the Romans’ unity with Christ continues on even though that unity has already taken place some time ago. When the Romans are exhorted to see themselves as “dead to sin and alive to God in Christ Jesus,” the idea is that they are to continually do this. This highlights their justification and unity with Christ that they already had and continue to have (see 1:8 where they are commended for their faith that is “proclaimed throughout the world”).