Psalm 23

A shepherd in Judah moved his flock daily. The hills are dry, the grass thin and scattered, so the animals had to be led from one patch to the next and down to water. Sheep will not drink from fast, noisy water — they are poor swimmers and their wool soaks and drags them under — so a shepherd dammed a pool or found a quiet stretch. "He leadeth me beside the still waters" is a job description.

The rod and the staff are two different tools. The rod was a short, heavy club, often studded, carried at the belt and used against predators — David told Saul he had killed a lion and a bear. The staff was the long crook, used to guide, to hook a straying animal, and to lean on across broken ground. The shepherd also "passed the flock under the rod" to count and inspect them one at a time.

"The valley of the shadow of death" describes the deep, narrow ravines cut into that country. A flock moved through them to reach fresh pasture, and the walls made them dark, echoing, and perfect cover for a predator or a raider.

"Thou anointest my head with oil" is veterinary before it is ceremonial. Shepherds poured oil on a sheep's head and into its nose to keep off the flies that lay eggs in the nostrils, and rubbed it into scrapes from thorns and rocks. In the last two verses the picture shifts from pasture to house: a host in that culture was bound to feed and defend a guest under his roof, even from the guest's enemies, and the anointing and the overflowing cup are how an honored guest was received.