Our religion consists of two major divisions, Saivism and Vaisnavism. The doubt arises as to whether we are speaking here of two separate faiths or of a single one.
Christianity too has two major divisions but people belonging to both conduct worship in the name of the same God. In Buddhism we have the Hinayana and Mahayana streams but they do not make two separate faiths since both are based on the teachings of the same founder, the Buddha.
Do Saivas and Vaisnavas worship the same god? No. However it be with ordinary Vaisnavas, their acaryas or teachers never go anywhere near a Siva temple. Their god is Visnu, never Siva. In the opinion of the worshippers of Visnu, Siva is also one of his (Visnu's) devotees. There are extremists among Saivas also according to whom Visnu is not a god but a devotee of Siva. How then can the two groups be said to belong to the same religion?
Are they to be regarded as belonging to the same faith by virtue of their having a common scripture? The divisions [sects] of Christianity have one common scripture, the Bible; so too is the Qur'an the common holy book for all divisions of Islam. Is such the case with Saivas and Vaisnavas? Saivas have the Tirumurai as their religious text, while Vaisnavas have the Nalayira-Divyaprabandham as their sacred work. For Saivas and Vaisnavas thus the deities as well as the scriptures are different. How it be claimed that both belong to the same religion?
Though divided into Saivas and Vaisnavas, we have been saved by the fact that the white man brought us together under a common name, "Hindu". But for this, what would have been our fate? In village after village, we would have been fragmented into separate religious groups- Saivas, Vaisnavas, Saktas, worshippers of Muruga, Ganapati, Ayyappa, and so on. Further, in these places followers of religions like Christianity and Islam would have predominated. Now two regions of our subcontinent have become Pakistan, Had we not been brought together with the label of Hindu, the entire subcontinent would have become Pakistan. The very same men who created Pakistan through their evil design and sowed the seeds of differences among us with their theory of two races- Aryans and Dravidians- unwittingly did us a good turn by calling us Hindu, thereby bringing into being a country called "India. "
So are we one religion or are we divided into Two faiths? The belief that Saivas and Vaisnavas have separate deities and religious works does not represent the truth. Though the present outlook of the two groups suggests that they represent different faiths, the truth will be revealed if we examine their prime scriptures. The saints who composed the Tirumurai of the Saivas and the Nalayira-Divyaprabandham of the Vaisnavas never claimed that these works of theirs were the prime religious texts of respective sects. Nor did they regard themselves as founders of any religion. Vaisnavism existed before the Azhvars and so too there was Saivism before the Nayanmars.
The original scripture of both sects is constituted by the Vedas. Saivas describe Isvara thus:
Vedanathan, Vedagitan, aranan kan
Similarly, the Vaisnava texts proclaim, "Vedam Tamizh seytaMaran Sathakopan. "If we pay close attention to their utterances, we will discover that the Vedas are the prime scripture of both sects. The Tevaram and the Nalayaira-Divyaprabandham are of the utmost importance to them (to the Saivas and Vaisnavas respectively); but the Vedas are the basis of both. The great saint-poets who composed the Saiva and Vaisnava hymns sing the glories of the Vedas throughout. Whenever they describe a temple, they go into raptures, saying, "Here the air is filled with the sound of the Vedas and pervaded with the smoke of the sacrificial fire. Here the six Angas of the Vedas flourish. " In the songs of these hymnodists veneration of the Vedas finds as much place as devotion to the Lord.
The Vedas reveal the One Truth to us in the form of many deities. The worship of each of these divine beings is like a ghat on the river called the Vedas. Sekkizhar says the same thing: "Veda neri tazhaittonga mihu Saivatturai vilanga. "
Apart from Saivism and Vaisnavism, there are a number of sectarian systems like Saktam, Ganapatyam, Kaumaram, and Sauram (worship of Sakti, Ganapati, Kumara or Subrahmanya and the Sun God). The adoration of these deities is founded in the Vedas, according to the Texts relating to them: "Our deity is extolled in the Vedas, " each system contains such a declaration.
Thus we find that there is but one scripture as the source common to the different sects and schools of thought in the Hindu religion.
This source includes the Upanisads. On ten of them (Dasopanisad) the great teachers of the Saiva, Vaisnava, and Smarta traditions have written commentaries. The Upanisadic texts proclaim that the Brahman is the one and only Godhead: In the Kathopanisad it is called Visnu; in the Mandukyopanisad it is called Sivam. All the deities mentioned in the Samhitas of the Vedas- Mitra, Varuna, Agni, Indra and so on - are different names of the same Truth. So it is said in the Vedas: "Ekam sad vipra bahudha vadanti. "
It emerges that for all the divisions in our religion there is but one scripture- a scripture common to all- and one Godhead which is known by many names. The Vedas are the common scripture and the Godhead common to all is the Brahman. Thus we can say with finality, and without any room for doubt, that all of us belong to the same religion.
The Vedas that constitute the scripture common to all and which reveal the Godhead that is common to us also teach us how to lead our life, and- this is important- they do us the ultimate good by showing us in the end the way to become that very Godhead ourselves. They are our refuge both here and the hereafter and are the source and root of all our different traditions, all our systems of thought. All sects, all schools of our religion, have their origin in them. The root is one but the branches are many.
The Vedas are the source not only of various divisions of Hinduism, all the religions of the world may be traced back to them. It is our bounden duty to preserve them for all time to come with their glory undiminished.
For a general background, please see here