I was heading for the final leg of my flight to Tel Aviv when something curious happened. As I crossed the Brussels airport, I was joined by other travelers. At each corridor, the crew swelled in size. Kippah-capped men carrying heavy briefcases, young couples wearing Star-of-David embroidered backpacks, older Hasidic rabbis who looked like Moses, families with infants in strollers and several toddlers trudging behind—we were all heading to the same place.

At the gate, I felt as if I’d crashed a family party. A couple of young...