The Reversed Ten Commandments
You are a lifelong Christian, and one day while home alone God appears before you. He assures you that he is in fact God, and has a new set of instructions for humanity. We must now all do precisely the opposite of what the Ten Commandments say. From now on, we must say his name in vain, steal from our neighbours, disrespect our parents, and so on. God assures you that this was his plan from the very beginning, and that these reversed commandments are now the morally correct thing to do. To go against them would be a sin!
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