11 Then Shmuel asked Yishai, “Are these all the boys you have?” He replied, “There is still the youngest; he is tending the flock.” And Shmuel said to Yishai, “Send someone to bring him, for we will not sit down to eat until he gets here.”
16:11 There is still the youngest; he is tending the flock
Young David is not the only great leader of the Children of Israel who was a shepherd before Hashem called him to a leadership role. For example, Moshe was also a shepherd. Shepherds bear great responsibility for the flock as a whole, and also for each individual sheep. Each one must be cared for, and must be counted as part of the flock for tithing. This is perfect training for leaders, who must lead the nation as a whole, and also maintain concern and compassion for each individual.