"Contemplating is receiving." (St. John of the Cross) What we receive in prayer is the Spirit, who makes all creation new, moment by moment. It is the Spirit who rebirths us within the caves of our hearts. The case is a metaphor for this silent withdrawal, this going away to be alone, to listen, to gestate the Spirit, to rebirth ourselves. The reborn self is the child of wisdom born in solitude.
If the phone rings, think of it as carrying a message
Larger than anything you've ever heard,
Vaster than a hundred lines of Yeats.
...When someone knocks on the door, think that he's about
To give you something large: tell you you're forgiven,
Or that it's not necessary to work all the time, or that it's
Been decided that if you lie down no one will die.