The Bible makes numerous analogies, regarding Gods people as sheep, and he as the Shepherd. Jesus was, for example the good shepherd, who layed down his life for his sheep.
No analogy is perfect. Still some analogies are a better fit than others. As W. Phillip Keller abundantly illustrates in his book, the Bible's Shephed/Sheep analogy is one of the best, and the lovely and beloved Psalm 23 perhaps its most sublime discourse.
But most people nowadays, have only passing familiarity with the life and habits of sheep. Keller, a former Sheherd himself sheds amazing new light to us who are "sheep-ignorant" that deepens one's appreciation for the analogy and brings to the believer additional comfort as we trust in our Shepherd.
One interesting turn in Kellers book is how he treats verses 5-6. I had always looked at these as a transistion from the sheep/shepherd analogy to a guest/host analogy. "You prepare a table for me..." Many have taught this psalm this way. Keller however treats this second half of the psalm as a continuation of the sheep/shepard analogy. He views the psalm as taking the reader through a year in a sheep's life, and the table, he likens to a messa--- a flat table of land that sheep are broght to, after some preparation, to graze contentedly. The head then, that is annointed with oil, remains a sheep's head... for which oil is applied to keep away the pesky insects that bother the sheep.
Is he right to continue the analogy in this manner. Well, I've thought about it, and you know it makes sense.
But either way, Keller's book will bring you new appreciation for this Psalm and indeed for the Lord, who I pray is your shepherd.
A nice easy read, that is very much worth the effort.