Before becoming a leader of the Jewish people, Moshe was a shepherd.
The Midrash recounts how one day, while Moses was tending Jethro's flock in the Sinai Desert, a lamb strayed from the herd. Moses chased it until it reached a spring and began to drink. When Moses caught up with the lamb, he wept, saying, "I didn't know you were thirsty!" Then he took the lamb in his hands and carried it back to the flock. God said, "You are merciful in caring for sheep—you will care for my flock, the people of Israel.""
Besides demonstrating Moshe's compassion, this incident contains another important lesson: Moshe realized that the lamb did not stray from the flock out of malice or wickedness - it was simply thirsty.
When a Jew turns away from his people, God forbid, it is only because he is thirsty. His soul seeks meaning in life, but the waters of Torah have eluded him. So he wanders through strange lands, seeking to quench his thirst.
When Moshe understood this, he was ready to be a leader of the Jewish people. Only a shepherd who doesn't rush to judge the runaway lamb, who is sensitive to the reasons for its desertion, can mercifully lift it in his arms and bring it back home.