NEW DELHI — Narendra Modi, India’s prime minister, is returning to power by an astonishing margin — defying expectations, leaving the political opposition gutted and securing nearly two-thirds of the lower chamber of Parliament.

This election has proved how wildly popular he really is, and Mr. Modi and his Hindu-nationalist Bharatiya Janata Party see a clear mandate to transform India for an additional five years. The big question Indians were asking Friday: What is he going to do with that?

Many ask that question in hope, approving of the way he and his allies have already enhanced Hinduism’s role in public life, or of how he moved to help the poor and update the economy — or of both. This is what he has been doing his entire political career, simultaneously pushing Hindu traditions and modernizing India. Most analysts believe he will continue along this path.

But there is a sizable chunk of India that voted against Mr. Modi’s party, and many members of this anti-Modi crowd are deeply worried about his having a stronger hand.