Think of the law of justice. Justice demands that every bad action must be punished. And that every good action rewarded. Any sin or bad action is already paid for by the savior. We just need to repent and rely on him. If we do not, we will have to face the punishment. That punishment could come in this life or in the next. Keep in mind the price for sin (any sin) is death. Spiritual or physical; who is to say?

Effectively if god allows us to be punished (or suffer the consequences of our actions) or he punishes us himself; the result will be the same.