For years, hip congregants at a popular Brooklyn Hasidic synagogue packed a raucous Purim party. The annual fete was the biggest event on Chevra Ahavas Yisroel's social calendar--until this year.

The congregation's rabbi, Yechezkel Denebeim, 28 years old, abruptly canceled the March 15 bash after he said he experienced an "awakening" during a recent trip to Israel.

The...