Charles H. Spurgeon on Psalms 23:4

"Rod and staff." The shepherd invariably carries a staff or rod with him when he goes forth to feed his flock. It is often bent or hooked at one end, which gave rise to the shepherd's crook in the hand of the Christian bishop. With this staff he rules and guides the flock to their green pastures, and defends them from their enemies. With it also he corrects them when disobedient, and brings them back when wandering. This staff is associated as inseparably with the shepherd as the goad is with the ploughman. W. M. Thomson.