More often than not when somebody throws out the “we’re not under law but under grace” phrase it’s either used to say, “Hey, come on! I’m a Christian so my sin’s not all that big of a deal,” or “Don’t give me any commands. That’s old-school, like Moses and the Old Testament era old-school.”
In light of this, we might forget that the phrase is actually tied to an exhortation for holiness, “sin will have no dominion over you.” That statement is both a fact based upon our dying and being raised in Jesus (Romans 6:1-13) as well as a reminder of what reality should look like in light of that fact: we shouldn’t let ourselves live under sin’s dominion (Rom. 6:15-23).
As someone who wants to daily find refreshment in free grace while also wanting to mature in Christ in a manner propelled by that grace, I find Romans 6:14 to be a huge help. It gives me an encouragement to pursue holiness without making either my energy in that pursuit or how far I make it in that pursuit the source of my confidence before God. Douglas Moo provides a helpful explanation as to why the indicative and imperative should neither be confused nor separated.
“‘Indicative’ and ‘imperative’ must be neither divided nor confused. If divided, with ‘justification’ and ‘sanctification’ put into separate compartments, we can forget that true holiness of life comes only as the outworking and realization of the life of Christ in us. This leads to a ‘moralism’ or ‘legalism’ in which the believer ‘goes it on his own,’ thinking that holiness will be attained through sheer effort, or ever more elaborate programs, or ever-increasing numbers of rules. But if indicative and imperative are confused, with ‘justification’ and ‘sanctification’ collapsed together into one, we can neglect the fact that the outworking of the life of Christ is made our responsibility. This neglect leads to an unconcern with holiness of life, or to a ‘God-does-it-all’ attitude in which the believer thinks to become holy through a kind of spiritual osmosis. Paul makes it clear, by the sequence in his paragraph, that we can live a holy life as we appropriate the benefits of our union with Christ. But he also makes it clear, because there is a sequence, that living the holy life is distinct from (but not separate from) what we have attained by our union with Christ and that holiness of life can be stifled if we fail continually to appropriate and put to work the new life God has given us. Jeremiah Bourroughs, a seventeenth-century Puritan, put it like this: ‘…from him [Christ] as from a fountain, sanctification flows into the souls of the Saints: their sanctification comes not so much from their struggling, and endeavors, and vows, and resolutions, as it comes to them from their union with him.'”
 Douglas Moo, The Epistle to the Romans (Grand Rapids: Eerdmans, 1996), 391.