Madelein L'Engle says it best in her book A Ring of Endless Light
Mother put her hand against Suzy's cheek. "I believe in prayer. You know that."
"But you don't even know Jeb! You've never even met him!"
"What's got into you?" John demanded sharply.
Suzy still sounded angry. "Prayer didn't keep Jeb from being hit by a motorcycle. It didn't stop Grandfather from having leukemia."
"Prayer was never meant to be magic," Mother said.
"Then why bother with it?" Suzy scowled.
"Because it's an act of love."