If prayer is the attempt to understand God, then grieving is the deepest form of prayer, rising from the body and soul and mind, asking God and really and truly wanting to know, no matter what the answer: Whoa re you? Why did you create a world with pain? Why is life this way? What are you? Because you are not what I thought you were.
Grieving, at its deepest level, is to acknowledge that creation can be cruel and that people suffer. To look at this truth, to allow yourself to feel it, you are forced to consider the nature of this world and this existence. You ask how this can be and who set this up and why this happens. To grieve is to ask God the hardest questions. To grieve is to ask who God really is. It’s to change your perspective on all other human beings and their relationships to one another and to you and your place in this world. To grieve is to start over, to be re-created.
Kerry Egan in Fumbling: A Pilgrimage Tale of Love, Grief, and Spiritual Renewal on the Camino de Santiago.