On Sunday, July 13, chants of “death to the Jews” could be heard during a rally of thousands of anti-Israel protesters in Paris. Soon after, a mob of the angry demonstrators attacked the Abravanel synagogue in Paris’s 11th district. They did not succeed in breaking in, but they did succeed in scaring the scores of men, women, and children who had gathered inside the synagogue for a peaceful memorial service for three teenagers who had been murdered in Israel by terrorists.

After hearing of this terrible incident, I called the president of the synagogue to express my solidarity. In turn, Serge Benhaim invited me and a colleague, Rabbi Etan Mintz, to spend the Sabbath with the synagogue and to deliver the sermon for the congregation on Saturday morning, July 19. I was honored to accept the invitation.

What I saw was a Jewish community under siege in a manner that I never thought I would experience. I had heard from my father about his experience in Paris in 1941 and how his life was endangered there as he was running away from the Nazis. But I never imagined that Paris would again become a city where synagogues would be torched and attacked by angry mobs. In the past two weeks, several synagogues and Jewish-owned businesses have been attacked, which occured in spite of heavy police protection for the Jewish community. What we are witnessing in Paris reminds us of the historical dangers posed by anti-Semitism to Europe’s Jews.

Last Saturday, the Jewish community in Paris canceled all classes and afternoon Sabbath programs because of safety concerns. At Arbrabanel synagogue, the rabbi quoted the rule that safety for one’s life comes before studying Torah. The police had asked that Jews not even walk the streets from 3:30 to 8:30 p.m. that day as they could not assure adequate protection in the face of angry anti-Israel protesters. I was told that wearing my traditional yarmulke in public could be viewed as an act of incitement and that the mob then would have legal protection. My hosts insisted that I wear a baseball hat over my yarmulke.

To reinforce the seriousness of this point, police in full riot gear were stationed outside the Abravanel synagogue. Later, I found out that the police, indeed, turned back a group that was intending to attack the synagogue again that Sabbath afternoon.

Everyone I spoke with felt that the Jewish community of Paris had no long-term future and that the question was not whether the community should emigrate but when and how.

In the meantime, all of us around the world must be vigilant on their behalf.

On the morning of July 19, more than 300 people bravely showed up at the Abravanel synagogue for Sabbath prayers.

I offered the congregation the following teaching from the Hassidic rabbi Nachman of Breslov (1772-1810): “The whole world is a very narrow bridge, but a person must live one’s life without any fear at all.”

Then, I said to them: “The times we are now in are moments of contracting. The bridges in our world are getting narrower, and life is harder than normal, but the main thing is to have no fear at all. We will not be afraid! The Jewish community around the world will stand in solidarity with you.”

As the service concluded the congregation spontaneously started singing the lyrics to this teaching of Rabbi Nachman. The singing soon led to robust dancing, with some worshippers openly weeping. The noise became so unusual that the police opened the gates of the synagogue to see what was going on. The police said: “Why are you singing if things are so frightening for you?”

Benhaim, the synagogue’s president, told the police that we were singing because even though things are very hard and very scary, we were rejoicing in the fact that we have each other and we have our faith.

Shmuel Herzfeld, a Modern Orthodox rabbi, heads the National Synagogue in Washington.