Will India remain a secular state committed to treating all faiths equally, or will it morph into an explicitly Hindu nation whose Muslim minority is kept in its place? A debate about migrants will help settle this fraught question.

The ruling Bharatiya Janata Party wants to fast-track Indian citizenship for non-Muslim migrants from neighboring countries while pointedly excluding Muslims. This foolish idea may win the BJP votes in the current election, but at the cost of undermining interfaith harmony, seeding long-term domestic...