Siddhantasara received positive reviews and became a landmark in the history of Gujarati literature but was also criticised because of the logical lapses and inconsistencies in the author's arguments.

Manishankar Bhatt (known as Kavi Kant) published his review as a book titled Siddhantasaranu Avalokan (Analysis of Siddhantasara).

Siddhantasara is considered by critics to be Manilal's most important work, and has been seen as a response to the cultural agenda and reform activities of colonial India at the time.

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.

[4] 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.

[7][8] In the first chapter, Manilal rejects the idea of the Genesis creation narrative as told in the Old Testament, and argues that the universe is eternal; that is, with neither beginning nor end.

[9] He attempts a logical explanation of the ritual practices described in the Vedas, their emphasis on Karma Marga, and their ideas of multiple gods and goddesses and of idol worship.

[13] The historian Vijay Singh Chavda [gu] wrote: "This work was the outcome of Manilal's long and thoughtful study of the fundamental principles of Sanatan Hindu Dharma and he placed them in their proper historical context".

[14] Thaker sees the publication of Siddhantasara as an event in Gujarat, saying that it corrected the impression among the educated class that the Puranas were merely fanciful stories.

He has been able to establish that the writers of the Puranas were, to large extent, conversant with the Vedas and the Upanishads, and that their objective was not to create superstition in the mind of the people, but to teach them truth of religion in a simple popular form.

[17]In the final installment of his letters, which appeared in August–September issue of Jnanasudha, Kant wrote: "I respectfully welcome this work of Manilal despite several contradictions, much one-sided reasoning and similar other faults ...