And they took offence at him. His very presence in the synagogue, “pretending” to be a spiritual leader, incited their wrath, and they were scandalized by his presence there as one who would presume to teach them.
They knew him from when he was but a boy, and here he was taking on more authority than he ought to, more than he was allowed to, given his history, given what they knew about him.
And the result, Mark says, is that he did not do many works of power there. Instead, Jesus marveled at their disbelief.