Like the tumultuous adolescent years of human development, the changes during the teen years of the 21st century disrupted American identity as we’ve known it. These transformations have come upon us quickly, upending long-standing assumptions — particularly among white Christians — about the American social fabric. And as with teenagers, they have created a lot of anxiety and fear about the future. Of all the changes to identity and belonging, the century’s second decade has been particularly marked by a religious sea change. After more than two centuries of white Anglo-Saxon Protestant dominance, the United States has moved from being...