If one be asked to point out the system of thought towards which as a centre all the ancient and modern Indian thoughts have converged, if one wants to see the real backbone of Hinduism in all its various manifestations, the Sutras of Vyasa [i.e. the Brahma Sutras] will unquestionably be pointed out as constituting all that.
Either one hears the Advaita-Keshari roaring in peals of thunder — the Asti, Bhâti, and Priya — (Exists (Sat), Shines (Chit), Is beloved (Ânanda) — the three indicatives of Brahman.) amidst the heart-stopping solemnities of the Himalayan forests, mixing with the solemn cadence of the river of heaven, or listens to the cooing of the Piyâ, Pitam in the beautiful bowers of the grove of Vrindâ: whether one mingles with the sedate meditations of the monasteries of Varanasi or the ecstatic dances of the followers of the Prophet of Nadia; whether one sits at the feet of the teacher of the Vishishtâdvaita system with its Vadakale, Tenkale, (The two divisions of the Ramanuja sect.) and all the other subdivisions, or listens with reverence to the Acharyas of the Mâdhva school; whether one hears the martial "Wâ Guruki Fateh" (Victory to the Guru) of the secular Sikhs or the sermons on the Grantha Sâhib of the Udâsis and Nirmalâs; whether he salutes the Sannyâsin disciples of Kabir with "Sat Sâhib" and listens with joy to the Sâkhis (Bhajans); whether he pores upon the wonderful lore of that reformer of Rajputana, Dâdu, or the works of his royal disciple, Sundaradâsa, down to the great Nishchaladâsa, the celebrated author of Vichâra sâgara, which book has more influence in India than any that has been written in any language within the last three centuries; if even one asks the Bhangi Mehtar of Northern India to sit down and give an account of the teachings of his Lâlguru — one will find that all these various teachers and schools have as their basis that system whose authority is the Shruti, Gitâ its divine commentary, the Shâriraka-Sutras its organised system, and all the different sects in India, from the Paramahamsa Parivrâjakâchâryas to the poor despised Mehtar disciples of Lâlguru, are different manifestations.
The three Prasthânas, ("Courses", viz, the Upanishad (Shruti), the Gita, and the Shariraka-Sutras [i.e. the Brahma Sutras].) then, in their different explanations as Dvaita, Vishishtadvaita, or Advaita, with a few minor recensions, form the "authorities" of the Hindu religion. The Purânas, the modern representations of the ancient Nârâsamsi (anecdote portion of the Vedas), supply the mythology, and the Tantras, the modern representations of the Brâhmanas (ritual and explanatory portion of the Vedas), supply the ritual. Thus the three Prasthanas, as authorities, are common to all the sects; but as to the Puranas and Tantras, each sect has its own.
The Tantras, as we have said, represent the Vedic rituals in a modified form; and before any one jumps into the most absurd conclusions about them, I will advise him to read the Tantras in conjunction with the Brahmanas, especially the Adhvaryu portion. And most of the Mantras, used in the Tantras, will be found taken verbatim from their Brahmanas. As to their influence, apart from the Shrauta and Smârta rituals, all the forms of the rituals in vogue from the Himalayas to the Comorin have been taken from the Tantras, and they direct the worship of the Shâkta, or Shaiva, or Vaishnava, and all the others alike.
Of course, I do not pretend that all the Hindus are thoroughly acquainted with these sources of their religion. Many, especially in lower Bengal, have not heard of the names of these sects and these great systems; but consciously or unconsciously, it is the plan laid down in the three Prasthanas that they are all working out.
Wherever, on the other hand, the Hindi language is spoken, even the lowest classes have more knowledge of the Vedantic religion than many of the highest in lower Bengal.
There are regional differences and there are sect differences. As Vivekananda points out, within Hindi speaking regions there is a great penetration of the advaitic school. Also as he points out, purana can mean different books to different sects.