"And he departed like a flock with them." Just as this flock cannot be fixed if they stray, so too Israel (Exodus 16:4), "And the people went out and gathered." Just as this flock damages trees without their owner being liable, so too Israel. Sometimes this flock is sheared and its wool and milk are used for its owner's benefit, so too Israel.
Rabbi Yochanan said in the name of Rabbi Eliezer, who cited Rabbi Yossi HaGalili (Ezekiel 34:31), "And you, my flock, the flock of my pasture, are men, and I am your God," implying that Israel are like a flock. Rabbi Shimon said in the name of Rabbi Yossi ben Ketzarta, and Rabbi Yudan said in the name of Rabbi Yehoshua ben Levi, in whose flock? In the flock of Jethro. In which herd?
In Jethro's herd. Just as Jethro's herd and flock traveled from the city to the wilderness, so too Israel. Just as this flock follows its owner, so too Israel follows Moses and Aaron, as it is stated (Exodus 15:22), "And Moses led Israel onward from the Red Sea."