In 1888, Manilal had planned to write two books in Gujarati.
The first of these was a book expounding on practical expressions of Hindu philosophy.
The second was a detailed treatise on the theoretical aspects of Advaita philosophy, in the context of a comparative study of Hinduism on the one hand and all other religions of the world on the other.
On 9 September that year he finished writing the first book, called Pranavinimaya, and it was published in December.
Pranavinimaya was based on mesmerism.
On 5 October, Manilal began writing the second book, Siddhantasara.
Progress was interrupted by illness, but the book was completed in March 1889 and published from Bombay in June 1889.
The book had a subtitle Sarvamanya Ekdharmana Tatva Suchavvano Prayatna (Towards a Philosophy of Universal Religion).

In the preface to Siddhantasara, Manilal clarifies his aim in writing the book:
There are many systems of thought — like religion and philosophy — in this world, but I believe that all these are the transformations of the same eternal principles.
The path of arriving at these eternal principles is the Advaita philosophy of ancient India.
I believe that this needs no proof, as it is its own proof.
My attempt here is to establish these principles.

— Manilal Dwivedi, 1889
On the title page, Manilal described the work as "an outline of the history of thought in India terminating with an attempt to point out the basis of a universal religion".
Manilal explained that his "attempt [was] to search for truth, which is not bound by any sectarian or ideological considerations", and suggested that this search for truth would be conditioned by his own beliefs.
In 1888, Manilal had planned to write two books in Gujarati. The first of these was a book expounding on practical expressions of Hindu philosophy. The second was a detailed treatise on the theoretical aspects of Advaita philosophy, in the context of a comparative study of Hinduism on the one hand and all other religions of the world on the other. On 9 September that year he finished writing the first book, called Pranavinimaya, and it was published in December. Pranavinimaya was based on mesmerism. On 5 October, Manilal began writing the second book, Siddhantasara. Progress was interrupted by illness, but the book was completed in March 1889 and published from Bombay in June 1889. The book had a subtitle Sarvamanya Ekdharmana Tatva Suchavvano Prayatna (Towards a Philosophy of Universal Religion).
In the preface to Siddhantasara, Manilal clarifies his aim in writing the book:
There are many systems of thought — like religion and philosophy — in this world, but I believe that all these are the transformations of the same eternal principles. The path of arriving at these eternal principles is the Advaita philosophy of ancient India. I believe that this needs no proof, as it is its own proof. My attempt here is to establish these principles.
— Manilal Dwivedi, 1889
On the title page, Manilal described the work as "an outline of the history of thought in India terminating with an attempt to point out the basis of a universal religion". Manilal explained that his "attempt [was] to search for truth, which is not bound by any sectarian or ideological considerations", and suggested that this search for truth would be conditioned by his own beliefs.
Siddhantasara