John Calvin Commentary Romans 6:15

"What then? shall we sin, because we are not under law, but under grace? God forbid." — Romans 6:15 (ASV)

What then? Since the wisdom of the flesh always objects loudly to the mysteries of God, it was necessary for the Apostle to add something to anticipate an objection. For because the law is the rule of life and was given to guide people, we tend to think that when it is removed, all discipline immediately collapses, restraints are taken away, and, in short, no distinction or difference remains between good and evil.

However, we are greatly mistaken if we think that the righteousness God approves in His law is abolished when the law is abrogated. For the abrogation in no way applies to the precepts that teach the right way of living, as Christ confirms and sanctions these and does not abrogate them. Rather, the correct view is that nothing is taken away except the curse, to which all people without grace are subject. Although Paul does not clearly state this, he does imply it.