Mike is intended to be like a messiah figure, beyond the shadow of a doubt. He is otherworldly, "from the heavens," and they almost immediately rule that Mike owns Mars, which means he has godlike status in their imagination. When he demonstrates that he literally does have magic powers which he can teach others to use, he is shown to be supernatural.
When he turns himself to learn about religion, he gains an exceptional grasp on the meaning of human life, and with his considerable enlightenment, he makes a religion about open-mindedness and tolerance (like Jesus), but since he didn't fit their outrageously prohibitive moral code (like Jesus and the Pharisees), they murder him. Heinlein even goes so far as to say that when Mike dies, he goes to heaven and becomes an archangel and he sits in the divine parliament next to his predecessors, Foster and Digby.
Now, let's see what exactly Mike died as a martyr for. Just before his untimely death, he was explaining to Jubal that he fears the religion he wants to bring to the earthlings is one they are unable to receive. His whole point was never to be licentious and indulgent (although he is often licentious and indulgent). His point was to show that human shame is an unnecessary aspect of human life, and that humans should just be happy and free.
This is Mike's final estimation of humanity before he dies and is seated in a position of honor in heaven. The point is quite simple: The novel rewards Mike for his correct verdict with divine authority. His assassination is merely the universe promoting him to a new rank. The novelist's opinion is pretty clear: Unnecessary religious shame prevents humans from attaining peace and happiness in life.
