In this chapter, Paul is emphasizing the objective reality of what Christ has done and stressing that it has overcome what Adam did, even going so far as to say in v. 20 that "where sin abounded, grace abounded all the more." If Paul had left off here, it would be easy to think that this was all very formulaic and automatic; Adam messed up the world, Christ fixed it. End of story. We might as well go on living our merry lives and, in fact, go on sinning while we are at it since our sin is what led to God's grace anyway. This is why Paul begins as he does in Romans 6.
"What shall we say then? Shall we remain in sin so that grace may increase?Paul answers emphatically "May it never be! How can we who died to sin live in it any longer?" The change that Christ has brought about in the world is not something external to us that doesn't involve us. The movement from that left column to the right one is not merely something Christ is doing in the world around us. It is something Christ wishes to accomplish in us. Paul believes that this is what happens in baptism. Just as Christ's faithful death and resurrection made the movement toward that right column a reality in our world, so also in baptism we die and are raised with Christ allowing us to move from the left column of sin and death to the right column of righteousness and life. For Paul, baptism is nothing less than a transfer of our being from one reality to another, an induction into a completely new way of being human. Paul's whole argument in this chapter rests on that premise. It is essentially "Given that we've been caught up in this entirely new reality in Christ, how can we possibly go back to the old one?"
Of course, the fact that Paul has to make this argument at all is the first indication that life, even in life in Christ, can never be as neat and tidy as two columns. Even though Paul believes that baptism is nothing less than the portal into this new way of being, he also knows that baptism does not guarantee a sinless life. It is not automatic. If it were, there would be no need anywhere in Paul's letters to correct his congregations or to say as he says here:
"Therefore, do not let sin reign in your mortal bodies...Do not present your members to sin as instruments of unrighteousness."Paul is emphatic that the victory has been won in Jesus Christ and that the way to participate in that victory is through baptism but he is just as emphatic that for all Christ has done he has not left us with nothing to do. The Church is called to "present yourselves to God as those who have been brought from death to life and your members to God as instruments of righteousness." Like soldiers presenting arms before a commanding officer, we are to present ourselves before God as those who are ready to carry out his mission of righteousness in the world.
I think any person with military experience would attest to the reality that simply signing papers to join the military isn't the same thing as being a trained soldier. To be sure, when you sign those papers your status has changed in a very real way. In that single act you have been transferred from the life of a civilian to that of a soldier and you are no longer your own master. But despite the very real change that has taken place, you do not suddenly become a combat ready warrior by signing your name. There has been a change of status that has tremendous consequences but it will take enormous amounts of discipline and training for that change in status to be fully realized.
I think that is something like what Paul is saying here. When we are baptized, our status really has changed but it would be foolish to think that all the consequences of that change will immediately and automatically take effect. Instead, we must continually choose to engage in discipline and training that will shape us into people who can be agents of God's redemptive movements in our world. We need worship, prayer, scripture, communion, fasting, service to others, Christian fellowship and all the other things we call "means of grace" and "spiritual disciplines" because these are our training, our boot camp. Baptism alone will not turn us into a people who imitate the faithfulness of Christ. We need the work of the Holy Spirit through these disciplines to be the people of holiness, mercy, compassion, and justice that we are called to be. Salvation is by grace but there is work to be done if that salvation is to be fully realized in our lives and the lives of those around us.