Ross Douthat has written perhaps the most important Catholic book in the era of Pope Francis, which began in 2013. To Change the Church is thoughtful, penetrating, and graced with an ironic touch and gentle humor. It is also terribly difficult for a faithful Catholic to review, as it is acutely critical of the pope. A disclaimer, then: Pope Francis is a holy man, for Catholics his teaching authority is infallible, and nothing contained here should be taken for filial impiety or disloyalty. Yet as Douthat notes, the principal duty of a Catholic isn’t to the pope but “to the...