Whether by plane, train or car, thousands of Jewish activists from all over the world made their way to the Crown Heights section of Brooklyn, N.Y., for the much-anticipated 25th annual International Conference of Chabad-Lubavitch Emissaries. The rabbis began trickling in on Tuesday as their flights landed at John F. Kennedy International Airport. More so than in years past, this year’s conference will shine a spotlight on Jewish unity. It takes place in a year of hakhel, a once in seven years occurrence that was marked during the time of the Holy Temple by a gathering of men, women and...