5ish, it’s amazing that a chassidus that deovtes itself to learning the Rambam can’t even parse a simple Rambam. The answer to your question is in the question itself: The king will be listened to BECAUSE HE IS A KING. And if you don’t listen to a king, you die. Simple. Only after he does all the things will he be Moshiach. But it won’t matter, because we listen to him due to his status of king, not of Moshaich.
BTW, the Rebbe was not a king, so he isn’t Moshiach.