Complex sentence: The congregation's membership dwindled throughout the 1940s and 1950s, limiting the services to holidays before finally closing when it could not steadily gather a minyin, ten men, in 1987.
Split into simpler sentences: The congregation's membership dwindled throughout the 1940s and 1950s, which limited services to holidays. The synagogue finally closed when it could no longer steadily gather a minyin, ten men, in 1987.