In a summer of sweaty, dirty, demanding volunteer work, one particularly arduous morning stands out. We were dismantling a Persian-period wall at Ashkelon. My job was to work the stones free with a pick and then carry them in my arms over a treacherous terrain of balks, pits and trenches. That was the first time I paid much attention to Denis and David.

They were as different as could be. Denis was 17, a blond-haired, blue-eyed Ukrainian in jeans and a T-shirt. David (pronounced dah-VEED), a dark-skinned Ethiopian, was about 60. He dressed in shorts, battered ankle-length dress boots, an oxford shirt buttoned to the neck and a green wool cap. But they had two important things in common: Both were Jewish, and both were olim—recent immigrants who had come under the Law of Return, which welcomes any Jew in the world to live in and to become a citizen of Israel.