We are two Jewish men who wear yarmulkes, the skullcaps that mark us in public as religiously observant. Neither of us came to that easily or early; our connection to Jewish faith and ritual deepened over the course of our lives—ebbing and growing along the way—until each of us, in his own time, chose to cover his head.But we were singled out as Jews long before we ever wore one. Antisemitism has never paused to ask whether a Jew believes in God or keeps the Sabbath—and neither do two Jews meeting for the first time, as that quiet flash of...