As a young boy, Rabbi Yosef Yitzchak (the sixth Lubavitcher Rebbe) would go with his father on walks through the woods. One time, as they talked, the boy absent-mindedly plucked a leaf off a tree and began to shred it between his fingers. His father saw what his son was doing, but he went on talking. He spoke about the Baal Shem Tov, who taught how every leaf that blows in the wind—moving to the right and then to the left, how and when it falls and where it falls to—every motion for the duration of its existence is under the detailed supervision of the Almighty. That concern the Creator has for each thing, his father explained, is the...