We can read the Twenty-third Psalm as a drama in three acts. Act one is serene, pastoral. The psalmist feels safe and secure, and he thanks God, his faithful shepherd, for providing him with that security. Act two turns dark and stormy. The psalmist's life is interrupted by trauma, tragedy, and bereavement. Instead of dwelling in green pastures by still waters, he finds himself alone in a dark valley. Then he learns that he is not really alone. He comes to see God not only as the source of the good things in his life, but as the source of comfort and consolation in hard times. He comes to understand that only because God was with him, he was able to find his way out of the darkness. He learns, as all of us who have gone through hard times learn, that the sunshine we step into when we have found our way through the valley of the shadow is infinitely sweeter than the sunshine we had basked in during our carefree, cloudless days. In act three, he realizes that his understanding of God, his relationship to God, has matured as well. God is no longer just the one who follows him through his travails. God now offers him something more permanent, an invitation to dwell in His house.
— Harold S. Kushner, The Lord Is My Shepherd