"I came bearing the Bhagvad Gita as a gift...I always present the Gita to eminent people I meet all over the world. When I met the (Japanese) Emperor I gave him the Gita because I have nothing more valuable to give and the world has nothing more valuable to get," the Prime Minister said, addressing the Indian community in one of his last engagements in Tokyo.
Mr Modi predicted there would be much reaction from his detractors in India. "There'll be a TV debate...All my secular friends will say 'don't know what Modi thinks of himself.' I don't know why such topics are debated," he said.
The Bhagvad Gita - a sermon on life's struggles and choices by Lord Krishna to Pandav king Arjun in the epic Mahabharat - is one of the holiest books of Hindus. Mr Modi refers to the Gita often. Other Indian leaders have too - Mahatma Gandhi famously called it his "spiritual dictionary."
Mr Modi's reference to likely criticism from "secular" quarters has context in rival parties like the Congress accusing him and his party, the BJP, of appeasing Hindu voters. Mr Modi draws his political roots from the Rashtriya Swayamsevak Sangh or RSS, a Hindu nationalist organisation.
In the run-up to the national elections which his party swept this year, Mr Modi focused his pitch for a mandate on development and the economy. But opposition parties allege that in that victory, the BJP drew benefit from the polarisation caused by communal violence in western Uttar Pradesh months before the national elections. The BJP won 71 of the 80 Lok Sabha seat in UP.
Rivals also allege that the ruling party has encouraged polarisation of voters in recent incidents of communal violence in states like Uttar Pradesh, where important by-elections are due.
Comments by RSS and BJP leaders and ministers in Mr Modi's government on India being a nation of Hindus has also created controversy.