There is one important distinction between the metaphor of father and that of shepherd. Children grow up and become less dependent on their earthly father, though the relationship continues. Sheep, on the other hand, are always completely dependent on their shepherd. They never outgrow their need for the shepherd to care for them, feed them, lead them, and protect them. The shepherd cares for the newborn lambs and is still there when the sheep grow old and weak. Therefore, the imagery of shepherd-sheep captures the comprehensive sovereignty of the shepherd over the sheep and the need of the sheep to yield completely to his care. The good news is that the Lord uses his sovereign power for the well-being of his flock.
Timothy Witmer, The Shepherd Leader: Achieving Effective Shepherding in Your Church (P&R, 2010), 13.