A makeshift memorial outside Pittsburgh’s Tree of Life synagogue on Thursday. (Gene J. Puskar/AP)

Melissa Fay Greene is the author of “The Temple Bombing,” about the 1958 bombing of the Hebrew Benevolent Congregation in Atlanta, and other books.

“At exactly fifteen minutes past eight in the morning, on August 6, 1945, Japanese time, at the moment when the atomic bomb flashed above Hiroshima, Miss Toshiko Sasaki, a clerk in the personnel department of the East Asia Tin Works, had just sat down at her place in the plant office and was turning her head to speak to the girl at the next desk.” So begins John Hersey’s “Hiroshima,” revealing how a sudden strobe light of unthinkable violence illuminates and freezes for all time the everyday motions of people caught in the glare.

Although there’s no comparison in scale, I thought of Hersey’s book as the news of the Tree of Life synagogue massacre broke over us, wave after wave of ever-more-specific details. The accumulating minutiae did not paint grander and more cinematic images of the events; quite the opposite — they brought into focus scenes ever more modest and homely: someone waited just inside the shul door to hand out prayer books to arriving worshipers; a small table stood ready with wine cups for the celebration of a bris; people looked forward to having a bite to eat together at a kiddush luncheon of challah, cheese, tuna salad and cookies. The emerging particulars gave us, among others, a retired accountant who loved the Pirates, a long-married elderly couple, a pair of developmentally delayed middle-aged brothers, a sprightly little lady closing in on her 100th birthday, and a 71-year-old man whose 1-year-old grandson was “the love of his life.” The social hall was mentioned. A storage room played a role.

The Jewish people know from social halls. I spent more of my childhood synagogue hours in the noisy basement linoleum-floored social hall under fluorescent lights than in the softly lit, carpeted sanctuary upstairs. The Purim carnival, the Hanukkah play, the bar mitzvah parties, the Shabbat luncheons of egg salad and rye bread and herring on paper plates at folding tables, with the kitchen in back and the mimeograph machine on a rolling cart in an adjacent storage closet. Synagogues, churches and mosques must all have these closets — windowless, narrow and tall, and lined with metal shelves up to the ceiling containing enough reams of paper in many colors for a decade’s worth of brochures.

Congregants were slaughtered in the social hall. Three of the Pittsburgh survivors hid out in the storage closet, while an elderly fourth also sheltering in there — perhaps confused — opened the door too soon and was murdered.

Even before the names of the victims were released — the number of dead clicking upward as hours passed — we knew who they would be. The first arrivals for Shabbat services tend to be the middle-aged and the elderly; at that hour, younger households are still corralling the children, trying to find the other shoe or the matching sock. The early birds tend to be the shomrim, the guardians of the congregation, the folks who — thanks to a long-ago yeshiva education — lead the morning service. As the terrible list of the dead was released, our hunch was proved correct: The early-arriving regulars had been mowed down. “The heart of our congregation,” said a fellow member. “They are the people who conducted our services, they did Torah readings, they managed the bimah.”

John Banville, in “Time Pieces: A Dublin Memoir,” writes charmingly of his childhood: “Certain moments in certain places, apparently insignificant, imprint themselves on the memory with improbable vividness and clarity.” His words returned to me this week, because it was precisely the “apparently insignificant” moments of an average Saturday morning in an average neighborhood in an average city that were irradiated by the klieg light of a terrorist attack. Was Joyce Fienberg wearing her double-strand of pearls that morning, or had she gone with the gold chain? Was Rose Mallinger planning to go out to lunch with her daughter after services? Some “apparently insignificant” moments proved lifesaving for the folks running a bit later than usual, still walking toward Tree of Life when strangers in passing cars, recognizing them as Jews, warned them to turn back to safety.

The wires had been crackling with warnings, the Internet sizzling with threats — against Jews and Muslims, African Americans and Latinos, gays and trans people, and anyone standing in solidarity or friendship with them. You can avoid the social media sites where the worst and most illiterate bigots type out the most vulgar of their thoughts and post the vilest of their imaginings; but you don’t have to click on Gab to know about these people, rubbing together the sticks of ignorance and gullibility and hatred, seeking ignition.

Sixty years and three weeks ago, the Temple in Atlanta was bombed by anti-Semitic white supremacists who perceived the Jews as “masterminding” the civil rights movement — not unlike accused killer Robert Bowers accepting the widely broadcast theory that Jews conceived and bankrolled the migrant caravan. The day after the Temple bombing, Ralph McGill, editor of the Atlanta Constitution, published an editorial attacking Southern elected officials who conjured up scapegoats and stirred up the mobs for their own political gains. “It is not possible to preach lawlessness and restrict it,” he wrote. “You do not preach and encourage hatred for the Negro and hope to restrict it to that field. It is an old, old story. It is one repeated over and over again in history. When the wolves of hate are loosed on one people, then no one is safe.”

When I wrote a book about the Temple bombing, I fell in love with that phrase, “the wolves of hate are loosed.” Yet since the Tree of Life killings, it’s somehow the second half of McGill’s sentence that modestly shows itself to me as the more important: “no one is safe.” It turns out that, when violence shatters the lives of innocents, the results are less likely to be epic and requiring of metaphor than to be composed of “apparently insignificant” moments. Those details become all the more precious to us because of how typical and homely they are, because they describe our very own lives, down to the satin yarmulkes in shiny colors, the tiny plastic cups sitting beside a wine bottle on the tarnished tray.

When hate speech, firing up the airwaves and popping at the rallies, suddenly tears apart — with homemade bombs or assault rifles — the everyday lives of ordinary people, the results are not cinematic or larger-than-life. The results are exactly life-size. Even a retired accountant standing in a storage closet may be murdered; even soft-spoken folks whose beloved dog is home waiting for its lunch may be destroyed. A clerk in the personnel department turns her face toward her friend at the moment the atomic bomb obliterates the Hiroshima sky. A bow-tie-wearing doctor, having sliced and arranged the bagels in a synagogue kitchen in Pittsburgh, hears strange noises and hurries through a doorway to see if someone needs help when his life ends in a blast of hatred and gunfire.