Towering over the bedraggled maze of shops and homes near Rath Yatra Chowk in Varanasi stands a 13-storey spanking new apartment building called Sevashram.

For the next month, the ground floor of the building will serve as Narendra Modi's campaign office.

With its manicured lawns and modern decor, the building fits the image Modi wants to sell to people here: A resourceful leader who will modernise the economy of the ancient city.

But in its foundation lies a more mystical history.

The building has come up on land owned by the family of Bhagwan Das, a Theosophist philosopher who wrote a book called The Essential Unity of Religions.

Theosophy is a tradition of Western esoteric philosophy that emphasises mystical experience and the underlying unity of things.

Founded in 1875 in New York with the aim of forming "a nucleus of the Universal Brotherhood of Humanity, without distinction of race, creed, sex, caste or color", the Theosophical Society moved to Chennai, and among the many Indians drawn to it was Bhagwan Das. He joined the society in 1894, becoming a close associate of Annie Besant, the British socialist turned Theosophist.

In a paper that he read at the Foundation Day of the Theosophical Society in 1911, Das said, "All the scriptures of all the nations of all times and all climes repeat the one teaching ‘Seek and find the God within’…The lost religions of Assyria, Chaldaea, Egypt, Mexico, Peru said it. The living religions of the Manu, the Zoroaster, the Buddha, the Jina, the Acharya Shankara, the Christ, the Prophet say it…In India, the latest great teachers of both Hindu and Musalman have nothing else to say."

In the paper, Das went on to quote Kabir, Bulle Shah and Nanak.

Latter-day scholars have unpacked the appeal of Theosophy among Western-educated Indians as a form of "neo-Hinduism" that "evoked an idealised past in which Indian society had been a pure and harmonious expression of this true, spiritual Hinduism". Romila Thapar, the prominent historian, sees "a close affinity" between the present-day Hindutva view and the theories of some Theosophists.

But in public life in the early 20th century, the Theosophists were far removed from sectarianism. Annie Besant joined the Indian National Congress. So did Das, born into a family of bankers, a member of Varanasi's mercantile elite.

"In Benaras, the city's commercial aristocracy, the Naupati bankers, gave rise to a succession of active Congressmen," wrote CA Bayly, the British historian. Das was one of them. He took part in the freedom movement, served as a member of Congress committees and was elected to the provincial assembly in 1934.

In Varanasi, Das helped Besant found the Central Hindu College, which later became the Benaras Hindu University.

In 1955, he was awarded the Bharat Ratna, along with Jawaharlal Nehru and M Visvesvaraya – the first Indians to get the country's highest civilian honour.

While Das's son, Sri Prakasa, was active in public life, serving as the governor of several states in the late 1940s and 1950s, the family has subsequently moved away from philosophy and politics and returned to its mercantile roots.

Today, Das' great grandson, Sameer Kant, lives in a plush apartment on the top-most floor of the Sevashram building. He run an investment firm and he speaks the apolitical language of money.

"I am an eternal optimist," he said, when I asked him about his future outlook on the country. "Whichever government comes to power, the economy would do well. Our long-term prospects are very good."

As a man of the markets, where is he putting his money, I asked him.

He laughed, declining to elaborate.

But later, he let slip where he thought the wind was blowing.

"Three prime ministers have come to this house – Jawahar Lal Nehru, Lal Bahudar Shastri, Indira Gandhi," he said. "Now we might soon have the fourth prime minister visiting." He was referring to Narendra Modi.

So how was it to have the Modi campaign office on the property of his great grandfather?

"It’s fine,” he said. “There is bound to be some nuisance. The day they had inaugurated the office, their workers messed up the garden with plastic cups."

On their part, the BJP campaign managers seem to have tried to make up for the nuisance by putting up a picture of Bhagwan Das outside the entrance to their office. It is a carefully selected picture: Das can be seen talking to Sardar Patel.

Click here to read all the stories Supriya Sharma has filed about her 2,500-km rail journey from Guwahati to Jammu to listen to India's conversations about the elections –  and life.