There is an interesting directive in Re’eh that forbids self-harming when mourning the passing of a loved one, a custom apparently common among ancient idolators.
Even more interesting is the Talmudic interpretation of this prohibition to forbid the factionalization of Judaism. This prohibition seems to demand complete conformity and uniformity among Jews.
So how is it that there are multiple customs and cultural idiosyncrasies within the Jewish world without this being a breach of the prohibition? What are the reasons behind this prohibition? When are we allowed to be different, and when are we not? And in a modern context, how is it halachically permitted to take part in Israeli elections that require us to back one party over another?
Rabbi Dunner looks at various sources to discover how this precautionary measure developed from Talmudic times, through the middle ages, and into the modern era, in order to get an understanding of this crucial mitzvah.