Since the initial objection to his attending came from members of the congregation, not the "Zionists", I wonder if this is going to be a private family party, not a community event. As a former congregation leader, my understanding is that the Bar Mitsvah was to celebrate a child's becoming an adult and taking on responsibilities for his own actions, in front of the community in which he lived. It will be interesting to see how many of the regular members of the synagogue are actually present.
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from the article: Goldstone to attend grandson's bar mitzvah as Zionist groups end feud