Elizabeth II

What is a queen for anyway? As the crowds cheer and rock stars gyrate next week to celebrate Elizabeth II's 50 years on the British throne, the question sounds churlish, even impertinent. Surely we should let the Brits have their fun, let the 76-year-old monarch—soul of probity and dutiful service—have her reward for a life sentence of grand ceremonies and banal conversations, without laboring to figure out why, in the 21st century, she ought to exist. But the question would not sound strange to Elizabeth herself. She has been grappling with it her whole life. And, in her implacable way, answering...