Can Hindu nationalism find a way to accommodate India’s religious diversity? It’s an urgent question as Bharatiya Janata Party leader Narendra Modi embarks on his third term as prime minister. If Mr. Modi can garner more support from the roughly 1 in 5 Indians who aren’t Hindus, he will strengthen his country and his party. If he fails to do this, his legacy will include a nation deeply divided along religious lines and a party whose sectarian politics severely limits its national appeal.

First, the bad news. Of the 240 BJP members of Parliament elected last month, not one belongs to India’s three largest minority religions: Islam, Christianity or Sikhism. Among Mr. Modi’s new 72-member council of ministers there isn’t a single Muslim—a rebuff to a 200-million strong community that accounts for 14% of India’s 1.4 billion people. Until midway through Mr. Modi’s second term (2019-24) every Indian government since independence in 1947 had included Muslim representation.

Part of the problem is ideological. Mainstream Indian nationalism, personified by Mohandas (Mahatma) Gandhi (1869-1948) and Jawaharlal Nehru (1889-1964), saw India as a multi-religious country united by a common quest for independence from the British. By contrast, the prominent Hindu nationalist ideologue Vinayak Savarkar (1883-1966) saw India essentially as a Hindu nation in which Muslim and Christian loyalties were suspect. In Savarkar’s view, groups whose “holy lands” (meaning Mecca, Rome or Jerusalem) were outside the Indian subcontinent couldn’t be fully trusted.