On the Sabbath, which starts at sundown on Friday, the Jewish tradition is to say a prayer while lighting two candles, attend synagogue and have dinner with family, along with prayers over wine and challah. On Saturday morning, Jews return to synagogue for services.

Mr. Harris said he saw no better place for people to show support for the Jewish community than at a synagogue, a space meant for peace and community that was turned into one of brutal violence in Pittsburgh last week.

At Park East Synagogue in Manhattan, clergy members are expecting a significantly larger crowd than on a typical Sabbath, said Benny Rogosnitzky, a cantor at the congregation. They plan to address the tragedy in Pittsburgh directly in a prayer and the rabbi’s sermon, Mr. Rogosnitzky said.

Since Saturday’s shooting, religious people outside the Jewish faith have found other ways to demonstrate their solidarity with Jews. For example, two Muslim organizations have raised more than $200,000 to help victims and their families following the massacre.

And Greg Zanis, a retired carpenter who has made tens of thousands of wooden crosses to memorialize the dead, traveled to Pittsburgh from Illinois this week to install 11 Stars of David near the Tree of Life synagogue. Mr. Zanis, who has been constructing such memorials for about 20 years, said he tried to honor all faiths — as well as those who did not subscribe to one during their lives.