In his introduction to chapter 6 of the Book of Romans, Thomas Schreiner--in his Baker Exegetical  Commentary--points to 3 things that lead to Paul's exhortation that they refuse the dominion of sin in their lives: 1) they have died with Christ; 2) they will be raised with Christ when they share in his resurrection; and 3) they have been freed from sin's dominion. Schreiner writes, 

The old powers of sin and death have been cannot triumph over them [believers]. They have been liberated from the power of sinand transferred into the realm of righteousness. In other words, the promises of triumph over sin that were given to Israel have become a reality in the new people of God. Since believers have died with Christ, will share his resurrection, and have been freed from sin's dominion, the are exhorted to refuse any dominion of sin in their lives.

These 3 facts rising from Christ's work of atonement, his work as the last Adam, are indeed facts. However, for the believer, they must often be engaged with as promises even as they were to Israel. Though this has been accomplished, it is often not they experienced reality of those who follow Christ. So, these promised must be "leaned into" with faith as the believer trusts in the redemption accomplished by the Son.