Chat during synagogue services and God might kill you, the Talmud warns.

That’s if you’re lucky. If you’re not, God might kill everyone you know: One legend attributes a 17th-century Cossack slaughter of tens of thousands of Ukrainian Jews to excessive talking in synagogue.

“Woe to people who carry on conversations during prayer, for we have seen many synagogues destroyed because of this sin,” one late 19th-century rabbinic commentator warned.

Despite these threats, Orthodox rabbis say they can’t control the crosstalk during their services. Reform rabbis, meanwhile, whose congregants generally don’t worry about divinely inspired massacres, say that they’re rarely interrupted by even a whisper.

This year, in the months before the High Holy Days, an anonymous activist has bought up pages and pages of ads in a Brooklyn Orthodox newspaper, urging Orthodox Jews to shut up in the pews. Yet non-Orthodox religious leaders say that the quiet they enjoy in their sanctuaries isn’t all that matters.

“Some people come to shul hoping to create a divine experience,” said Joey Weisenberg, music director at the Kane Street Synagogue, a Conservative congregation in Brooklyn. “Other people come to see their friends and hang out. Both of those things are important.”

Excessive talking is a fixation among some Orthodox rabbis. Jewish law explicitly bans talking during certain parts of the service, and some synagogues even read a special prayer for those who refrain from talking. Yet talking during the service is a persistent problem throughout the Orthodox world. (Rabbi Josh Yuter, who leads the Stanton Street Shul, a small Orthodox congregation on Manhattan’s Lower East Side, recalled visiting a synagogue where congregants talked through the prayer for those who refrain from talking.)

“It’s serious,” said Rabbi Asher Lopatin, newly appointed president of the left-leaning Modern Orthodox rabbinical school Yeshivat Chovevei Torah and former spiritual leader of a Chicago congregation. “I do think there are some synagogues where the rabbi just gives up.”

Certain Orthodox synagogues are worse than others. Large congregations can be noisier, though small congregations aren’t exempt.

And the problem isn’t limited to the Modern Orthodox. “It’s definitely an area where we have to improve,” said Ezra Friedlander, a New York-based political consultant who belongs to a Hasidic community in Brooklyn’s Boro Park. Friedlander takes it upon himself to shush the loudest talkers in the synagogue of the small Hasidic sect his father leads.

“It bothers me,” Friedander said. “God really does not appreciate when they talk.”

Some suggest that the problem stems from the length of the Orthodox service and the slack periods between important prayers. Others blame the comfort of Orthodox Jews in the sanctuary.

“Our congregations feel so at home in the synagogue that they lose some of the fear, reverence, that makes you not talk,” Lopatin said.

A search on the website of the Orthodox Union returns pages of articles about the problem. One goes so far as to effectively blame fathers who talk in synagogue for driving their kids away from Orthodoxy.

The talking problem has inspired jokes often told by rabbis. In one classic of the genre, told to the Forward by Rabbi Laura Geller of Temple Emanuel of Beverly Hills, a rabbi asks a pious Jew and an atheist why they attend synagogue. The pious Jew says that he comes to talk to God; the atheist responds that he comes to talk to the pious Jew.

For one anonymous advertiser, it’s all gone too far. Since early summer, someone has taken full-page anti-talking ads in successive issues of Flatbush Jewish Journal, a weekly paper circulated in Orthodox neighborhoods in the broader New York area. “Stop the Talking in Shul!” the ads warn.

One week, an ad in the series alleged that only “a fool” would talk during services. “It’s wrong! And we all know it,” another ad in the campaign read.

For the most part, the ads offer positive reinforcement for those who keep quiet in the pews. Not talking in synagogue, the ads promise, will bring “parnassah, shidduchim, refuos & yeshuos!” — that is, wealth, marriage, health and miracles. The advertiser asked readers to email them at StopTalking@gmail.com with stories of how their lives changed for the better after they stopped talking in synagogue.

An e-mail sent to that address went unanswered.

(An August 22 notice in the Flatbush Jewish Journal alerted readers that a version of the anti-talking ad in the previous issue accidentally included the name of God rendered in Hebrew and therefore could not be thrown in the garbage.)

The talking issue isn’t a problem in most Reform congregations.

“I never notice, if it is happening,” said Rabbi Anthony Fratello, spiritual leader of Temple Shaarei Shalom in Boynton Beach, Fla., a Reform synagogue.

That’s in part because silence in the pews is written into Reform Judaism’s DNA. The very character of the Reform service is, in part, a reaction to the problem of talking in Orthodox synagogues.

“They wanted to promote decorum,” said Jonathan Sarna, a professor of Jewish studies at Brandeis University and an expert on the history of American synagogues, of the early Reform congregations in the United States. “In America, houses of worship are open and people visit one another, and non-Jews often were appalled [by Orthodox synagogues], especially if they were Protestant [and] used to a very decorous, quiet, performance-oriented worship.”

In response, Reform Jews shortened the service, believing it would be easier to maintain discipline for an hour than for five hours. Organs were purchased for Reform synagogues specifically to discourage chatter.

“Many of these folks were in the process of moving into the middle class; they were moving up economically, and they themselves wanted to be respected by their neighbors,” Sarna said.

These sorts of serious, organ-heavy services can still be found in some Reform congregations. Others are looking to split the difference between the stodgy Cleveland-style silence and the Orthodox unruliness.

Weisenberg, who is attached both to the Conservative movement and the related independent minyan movement, recognizes the value of talking in synagogue. He also sees the value of silence. “If we walk in and treat [the synagogue] like a kind of space that could be holy, could be divine, it has a chance of becoming such,” he said.

“What I’m looking for in any fight against talking — I’m not looking for decorum, I’m looking for a subtle focus,” Weisenberg said.

For the anonymous advertiser behind the Flatbush Jewish Journal ads, that subtle focus may be drowned out by all the chatter.

“The sin is too large to bear,” the ad warns the readers.

Contact Josh Nathan-Kazis at joshnathankazis@forward.com or on Twitter, @joshnathankazis