Albert Barnes on Romans 6:15

What then? shall we sin, etc. The apostle proceeds to notice an objection which might be suggested. "If Christians are not under the law, which forbids all sin, but are under grace, which pardons sin, will it not follow that they will feel themselves released from obligation to be holy? Will they not commit sin freely, since the system of grace is one which contemplates pardon, and which will lead them to believe that they may be forgiven to any extent?" This consequence has been drawn by many professing Christians; and it was well, therefore, for the apostle to guard against it.

God forbid. Rom 3:4.