Union with Christ breaks the power of sin, diminishes its practice, empowers righteous living, and ensures progress therein. This transfer of power from sin to Christ definitive, and the believer simultaneously begins his progress in practical sanctification. 

A number of passages bear out these truths. First, in Romans 6, “our old self was crucified with Him” in order that “we too might walk in newness of life” (Romans 6:4, 6). On this basis, Paul commands us to consider ourselves dead to sin and alive to God and to live in accord with these realities (Romans 6:11–14). The believer obeys so “that the body of sin might be brought to nothing” (Romans 6:6), that is, so that the influence of sin upon the whole person might be eliminated altogether. Righteousness reigns in sin’s place (Romans 6:12–13).

Second, in Colossians 3, “you have put off the old self with its practices and have put on the new self” (Colossians 3:9–10). Again, these truths ground Paul’s commands for the believer to mortify his vices and clothe himself with virtue (Colossians 3:5–9a, 12–17). The believer’s experience of virtue grows over time: “the new self… being renewed in knowledge after the image of its creator” (Colossians 3:10).

Third, Ephesians 4 uses similar language: “You… were taught… to put off your old self… and to put on the new self” (Ephesians 4:21–22, 24). While Paul’s infinitives seem to be commands at first glance (to put off, to put on), they are better understood as recalling the content of what he taught the Ephesians, namely, that they had definitively put off the old man and put on the new, providing the basis (“Therefore” in Ephesians 4:25) for the imperatives in Ephesians 4:25–32. In so doing, they would progressively “be renewed [present tense] in the spirit of [their] minds” (Ephesians 4:23). 

Other passages use different terminology to speak to this decisive transfer of power, give imperatives, and describe the process of sanctification. 

First, 2 Peter 1 tells us that we have decisively “escaped from the corruption that is in the world” and have been “granted… all things that pertain to life and godliness” since we have “become partakers of the divine nature” (2 Peter 1:3–4). “For this very reason,” he commands, we should “make every effort to supplement your faith” with godly qualities (2 Peter 1:5–7). As we do so, “these qualities are yours and increasing,” making us effective and fruitful “in the knowledge of our Lord Jesus Christ” (2 Peter 1:8). 

Second, in 1 John 3, “because he has been born of God,” the child of God no longer “makes a practice of sinning” since such a life is “of the devil” (1 John 3:8–9). Instead, he “practices righteousness… as he is righteous” (1 John 3:7). John’s imperative is not so much to practice righteousness as it is to assume that believers will practice righteousness and to “let no one deceive you” about the matter (1 John 3:7; cf. 3:1–10).