A common theory about freedom of religion suggests that such a value is grounded in a modus vivendi, or compromise: People agree to respect each other's freedom in order to avoid religiously motivated strife. But the modus vivendi theory obscures the deep ground of principle on which the right of religious liberty rests and the true reasons for respecting the religious freedom of others.

As a Republican and a Democrat on the U.S. Commission on International Religious Freedom, we are committed, with our colleagues, to advancing...