After the careful description of the problem, Alma declares the glorious truth that the solution is provided. There “is a law given.” There is “a punishment affixed.” There is “a repentance granted.” There is mercy. There is justice because of the application of the law, and law exists because “law inflicteth the punishment.” Alma ties this entire logical string together with the declaration that it is integral to God. Were this entire string of logical to be untrue, “God would cease to be God,” an inconceivable notion. The argument for Corianton not only shows the logic of this understanding of the plan, but connects it to the very definition of God. If Coriantion believes in God, he must therefore believe in this plan.
The point here, of course, is to continue to build Corianton’s understanding of the place of punishment in a plan of happiness. The typical Nephite apostasy did not deny God, but rather the Atoning Messiah. What Alma has done is show that Corianton’s belief in God requires him to accept the Atoning Messiah, and particularly the aspect of the plan that has punishment for the breach of God’s laws.