In v12-14, Paul concludes that before being united to Christ, we presented ourselves to sin because we were living as dead and under the law, now under grace, we are raised to life and are free to (and exhorted to) offer ourselves to righteousness.

1.  Before union w Christ: sin reigned and we obeyed [him] toward unrighteous purposes. Our position was dead to God, and our hope was in law.
2. After union w Christ: Christ reigns and we obey [him] toward righteous purposes. Our position is alive to God, and our hope is in grace.