NEW DELHI — Addressing a euphoric crowd Friday afternoon, Narendra Modi rallied the public to join him in taking on challenges of a vast scale. He has floated the idea of building “a hundred new cities,” of extending a high-speed rail network across the subcontinent and undertaking the herculean task of cleaning the Ganges River.

He has been inspired by China’s model of high-growth, top-down development. But the country he will govern is India: messy, diffuse and democratic.

Mr. Modi’s Hindu nationalist Bharatiya Janata Party won a historic mandate in the country’s general election on Friday, emerging with 282 of 543 parliamentary seats, more than enough to form a government without having to broker a post-election coalition.

For months, Mr. Modi’s advisers had focused on crossing such a threshold, which they regarded as a signal that the country was behind an agenda of radical change.