I enjoyed this story, the world of the story seemed very strange, and I liked the imagery in this, but I seem to be running into the same issue of finding the ending confusing as a few other readers.
All in all, I think I have figured it out, as kind of being a reversal to a story like "Harrison Bergeron"? (I.E. Someone with a gift is burdened by a society that wants to keep him down, he rebels and is murdered. As opposed to someone with a gift goes on a selfish journey to try to master it, only to be burdened and held back by his family to keep him from rebelling, and by extension dies, at least in their ability to perform the gift.)
I guess I was just confused by their reaction, why bury him? Why not let him go off on his selfish parade? Didn't really seem like his was really hurting anyone to warrant death by living burial.
I understand there are probably metaphors here, but what are they? If we look at it symbolically, someone who has an amazing gift, or thinks they do, leaves their family to try to master the gift, the family doesn't desire them to do so, so they keep them down to try to keep them for reaching for selfish dreams, because they'd rather have them there, than away chasing their selfish heart.
I guess I am either interpreting a "Your family is bad and will not understand you and try to hold you back at all costs".
Or a, "You shouldn't abandon your family to chase your dreams even if you do have a gift" message, which seems to lean towards the latter since the author stated that Michael was supposed to be seen as a selfish jerk.