The main theme might revolve around the unknown. The Jax in the story, whatever it is, along with the moon which is often associated with mystery, could create a sense of fear in the wise man. It could also be about how wisdom doesn't always protect one from being afraid of certain things. For example, the wise man might have all the knowledge but still be fearful when faced with the situation involving Jax and the moon.
It could be that the main theme is the confrontation between a wise man's rationality and his irrational fear. The moon is often a symbol of the subconscious and the mysterious in many stories. And Jax, which is an unknown entity here, might represent something that challenges the wise man's understanding. So the story could be about how he deals with this fear that goes against his wisdom, whether he overcomes it or succumbs to it.