My mother often referred to a prayer that her mother said (in Swedish) nightly at the bedsides of her eight children as they headed off to sleep. The prayer became so embedded in their memories that one of her brothers, when he was dying 80 years later, asked my mother to "pray the prayer that Mama used to pray."

Like my dying uncle, many of us have simple lines of thoughtful prayer to which we cling when life becomes rough. The Lord's Prayer is an obvious one. Or some version of the "Jesus prayer": Lord Jesus Christ, have mercy on me, a sinner. Or the so-called prayer of St. Francis of Assisi that begins, "Lord, make me an instrument of thy peace …" (as much as one senses the spirit of Francis in the prayer, it is highly improbable that he was its creator).

Throughout the years of my Christian journey, I have used Psalm 23 as a prayer, and there have been sleepless nights when I have repeated the Shepherd Psalm over and over, perhaps as many as a hundred times. The vision of green ...