A point of fascination is that it’s never made clear just why the family was expelled from their community. What were the theological differences they had?
The father's message to the community seemed to be that his family was more devout than the rest of the community, but leaving it ambiguous was an excellent choice. We weren't meant to know if the family was overly pious, or had some evil predilections, that led to their decision to leave. There were subtextual cues that the lad had incestuous feelings toward his older sister, so perhaps we were meant to draw an inference from that.