A young Talmud scholar moves from Lithuania to London. Years later he returns home to visit his family.

His mother asks: “Yossele but where is your beard?”

“Oh, mama, in London, nobody wears a beard.”

“But do you at least keep Shabbat?”

“No, mama, in London people work all the time. We have to make money.”

“Oy vey. But do you still keep kosher?”

“Mum, I’m sorry, kosher food is expensive and hard to find.”

“Yossele…” she says. “Are you still circumcised?”

Thus joke points to a perennial Jewish anxiety: will people stay Jews? Will Judaism continue?

In every generation, a study is published, fearfully proclaiming that Jewishness is declining, which will be swiftly followed by rabbinic pronouncements about how to save it, philanthropists putting money into projects that engage young Jews, and various pundits proclaiming that this proves exactly what they had always said.

Why, when this problem has been repeatedly highlighted, has Judaism nevertheless continued, and Jewishness never seen the burial it was foretold?

For starters, it turns out that many of the things that people assured us would mark the end of Judaism were not that threatening after all. At the start of the Enlightenment, Orthodox leaders agonised that, if Jews went to universities, they would be needlessly subjected to heretical ideas and turn their backs on religion. In the end, Judaism and academic study proved more than compatible.

The fear about Jews losing their beards turned out not to be so troubling either. After all, half the Jewish people had never been able to grow them! In the 90s, the great moral panic centred on mixed marriages, which, experience has shown, only grew the Jewish population, rather than diminishing it.

So, why all the worry? In fact, these concerns undoubtedly go back to the beginnings of Jewishness. In the book of Ruth, we read a story of a young woman faced with the choice of whether to remain with the Jewish people. Either she could stay with her mother-in-law and run the risk of never marrying; or she could return to her original village and begin her life again.

Being Jewish was the harder option. Being Jewish was riskier and unknown. Ruth’s sister, Orpah, chose to leave the Jews and rebuild. Ruth chose Judaism.

She must have seen something in it that made her want to stay. Perhaps it was the God, or Naomi, or the people, or the way they lived. Judging by what she said, it was a combination of all of these. She chose the harder option, because it was the more beautiful one.

That has always been the way with Judaism. High risk. High reward. Hard to maintain. Worth maintaining.

That is why we feel anxiety about Jewish continuity. We know that it is not the easy option. It takes work. So we look around for people who will do it.

Our rabbis understood this feeling well. They told a story of the revelation at Sinai: that, on the day when God gave the Israelites the commandments, God raised Mount Sinai over their heads and told them to accept them. If they took them on, they would live. If not, the mountain would come crashing down on their heads and make the desert their grave.

“Choose life” wasn’t advice. It was a threat. Of course, they accepted.

But, said the rabbis, there were other times when they took on the commandments too. When there were no threats from God but plenty from the ruling powers. They point to the story of Esther, when the Jews lived under Persian imperial rule and could have been slaughtered for practising their religion. God did not appear to make promises or offer consolation. But they chose Judaism anyway.

This is a narrative of how Judaism has been continued. On an individual level, this is what happens to many of us. As children, we go to synagogue because our parents tell us to. We live their ways and eat their food because we have no other choice. Now, as adults, we turn up because we want to. There is no compulsion to attend. We do it because we have found in it something beautiful and worthwhile.

This is true, too, of our history as a community. There was a time when we had no choice but to be Jewish. Think of the periods when Jewishness was stamped on our passports and our job application papers; when being Jewish determined what jobs we could do and where we could live. We kept up Judaism because we had no other choice.

But now we have reached a time when it is a choice. Nobody is making us be Jewish. We sustain it because we want to. You who have turned up this morning could have gone anywhere. You could have done anything. But you chose to come here. Like Ruth and Esther, you decided that something in Judaism was beautiful and worthwhile.

You decided that this religion and these festivals have meaning. That is why I’m not really worried about Jewish continuity. I know that you are keeping it alive. I know that, in every generation, as long as there are a good few people who think Judaism is worthwhile, it will be.

On Shavuot, we renew our covenant with God. We take on the Torah once more. We decide to keep the flame of Jewish truth burning.

And, because of that, Judaism lives on.