The opening verse of the sixth chapter of Paul's letter to the Romans poses a question to the theology of grace which our Paul has been expounding until this point: What then are we to say? Should we continue in sin in order that grace may abound? (Rom 6.1). Paul's answer, of course, is the Greek equivalent of "Hell nah, dude!" But the precise nature of his response is fascinating, and worth considering at a little length.
His reasoning is this:
How can we who died to sin go on living in it? Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? Therefore we have been buried with him by baptism into death, so that, just as Christ was raised from the dead by the glory of the Father, so we too might walk in newness of life. For if we have been united with him in a death like his, we will certainly be united with him in a resurrection like his (vv. 3-5).
Paul's argument here is that baptism has united us with Christ in a critical way, so that it effectively gives us a new identity and a new nature of sorts. Christ once was under the same afflicting powers to which we are subject -- sin and death and temptation and the rest -- but he conquered them all, and with his resurrection is free of them forever (vv. 7, 9-10). Baptism, therefore, is a means given to us to unite ourselves to Christ and to benefit from his accomplishment for us! It is a real union with him, one which has efficacy to destroy the power of sin within us and which radically changes who we are and how we define ourselves. It gives us a new identity: we are no longer in slavery to sin, awaiting the wrath of God, but we share in the victory of Christ over all the powers of evil!
Note what Calvin has to say:
Let us know, that the Apostle does not simply exhort us to imitate Christ, as though he had said that the death of Christ is a pattern which all Christians are to follow; for no doubt he ascends higher, as he announces a doctrine, with which he connects, as is evidence, an exhortation; and his doctrine is this -- that the death of Christ is efficacious to destroy and demolish the depravity of our flesh, and his resurrection, to effect the renovation of a better nature, and that by baptism we are admitted into a participation of this grace. This foundation being laid, Christians may very suitably be exhorted to strive to respond to their calling (Commentary on Rom 6.4).
Oftentimes I encounter a kind of pessimistic self-evaluation on the part of Christians with regard to their spiritual and moral lives. They don't think they are all that great, they are gravely sinful, and they don't call attention to themselves; they may even use provocative adjectives in describing themselves. Certainly there is a place for realism about ourselves, and I speak lowly about myself as well. But Paul has a kind of optimism about what we are capable of, an optimism grounded in our real union with Christ through baptism: So you also must consider yourselves dead to sin and alive to God in Jesus Christ. . . . For sin will have no dominion over you (vv. 11, 14)
In fact, Michael J. McClymond notes in his chapter "Mission and Evangelism" in The Oxford Handbook of Evangelical Theology that what won over the Greco-Romans in the early ages of the church was precisely the radically different and morally stringent lifestyle of the Christians:
What Greco-Romans responded to was the Christian way of life. The perceived moral excellence of early Christians, their deeds of mercy toward those in need, and their reputation as healers of the sick and exorcisers of demons combined to make the gospel plausible in a cultural context seemingly inimical to the message. Paradoxically, it was the early Christians' fierce renunciation of Greco-Roman lifestyles and values that gave them credibility and esteem. . .
If we are to be effective witnesses for the gospel in our day and age as well, why should it not be in the old and tested method? Why shouldn't it be through a life lived in keeping with Jesus Christ's commandments? Everyone who looks upon Christ and the tireless love he displayed for all acknowledges his goodness and sees his value. Paul tells us we are united to this Christ in baptism so that we can live as he does. What better empowerment for evangelism can there be than that?