Christ is, under God, the moral Governor of the universe and planet Earth is in open mutiny. That there is a moral government cannot be denied. Our nature and circumstances demand that we should be under a moral government. For God to create free moral agents, with the ability to obey or disobey, and then not govern and reward their choices is foolish at best. Moral government is indispensable to the highest well-being of the universe of moral agents.
All laws have their penalties for disobedience, and the moral law is no different.
To say that a Christian can be in sin and yet not be under the penalties of sin is absurd. First there is spiritual death, which is separation from God and His favor. This Divine displeasure is revealed in the withholding of union and communion with God, answered prayer, strength, joy, peace, Divine healing, and a multitude of other benefits. Furthermore there are many physical and spiritual curses and calamities that come upon the sinner. God curses the sinner so that the sinner will repent of his sin and be blessed.