Or God to those under grace even today?
Indeed. As he says a little later in verse 15, "What then? Shall we sin because we are not under law but under grace? May it never be!"
The mere thought of such a thing was just incomprehensible to Paul. And yet, 2000 years later we still have folks who insist that if we actually believe that we are no longer under the law but under grace, that it means we will just sin like the devil. Incredible really.