VAIDIKA SAIVA SIDDHANTA.
It is mentioned in Jabala Upanishat that
"Brahmacharis said, tell us by repeating what, Amritatva will be for us? Upon which, Yajnavalkya answered, By repeating Satarudriya; these (contained in Satarudriya) are the names of Amrita, by (repeating) which one will become Amrita."
So the names mentioned in Satarudriya are those of Siva (Amrita) which are the means of producing Amritatva (Sivatva). The word Amrita is found in the following Upanishats as the name of eternal Siva:-
Isavasya II, 14.
Kena, 2, Khanda 12, 13.
Katha 5,8; 6.1, 14, 15, 17.
Prasna 1.10; 2.5; 3.11, 12; 5.7; 6.5.
Mundaka 1.2.11; 2, 2.2.5, 7,11; 3.2.9.
Aitaraya 4.6; 5.4.
Taittriya 1.6, 1,2; 3.10.3
Chandogya 1.4.4, 5; 3.12.6; 4.15.1; 7.24.1; 8.3.4; 8.7.4; 8.8.3; 8.10.1; 8.11.1; 8.12.1; 8.14.1.
Brihadaranya 4.4.2; 4.5, (1-14); 5.7. (3-23); 6.4.7, 17; 7.14.8.
Kaushitaki 3.2, 8.
Maitri 6.22, 24, 35.
In Mandukya the word Siva is found in 7,12. Although the word Amrita means nectar, water, milk &c., in some other places, in the srutis quoted above it denotes Siva only. Therefore all the above twelve principal Upanishats belong to Saivaism only.
Svetasvatara, Mahanarayana, Kaivalya, Kalagnirudra, Atharvasiras, Atharvasikha &c., clearly show that they are Saiva Upanishats. It is said in 14th Adhyaya of Jnanayoga Khanda of Sutasamhita,
"Some skilled in Vedasiras call the besmearing the whole body with sacred ashes as Pasupata; others call it Sirovrata; others, Atyasrama; others, Vrata and Sambhava."
That is: besmearing the body with the sacred ashes and repeating six mantras is called Pasupata in Atharvasiras; in Mundaka (3.2.10) Sirovrata; in Svetasvatara (6.2.1) and Kaivalya, Atyasrama; in Kalagnirudra, Vrata and Sambhava.
Sivarahasya says "Those belong to Taittriya think, O Uma, that sacred ashes should not be neglected."
The word Bhuti (sacred ashes) is found in Taittriya 1,11.1.
Again the Sutasamhita says (30th Adhaya, Yajnavaibhava Khanda) "Besmearing the whole body with sacred ashes and wearing on the forehead and other limbs with three streaks of ashes from appendages to knowledge (Para Vidya).
The 17th mantra of Isavasya and Brihadaranya (7. 15.1) enjoin "Besmear the body with ashes repeating "Agni is the ashes, Vayu is the ashes, Jalam is the ashes" (i.e. adding the word Bhasma at the end of the words Anilam, Vayu, Amrita as in the order mentioned in Atharvasiras). As besmearing the body with sacred ashes forms an appendage to the study of Upanishats and Brahma Sutras, Brahmins should observe the Pasupata Vrata. This is taught in the Pasupata Vrata Adhikarana (Saiva Bhasya, III.4.48, 49), Kailasa-Samhita, Linga-Purana, Vayu-Samhita, Maha-Bharata &c. By the reasons cited above, all the principal Upanishats and the Brahma Sutras founded upon them are in favor of Saivism and define the attributes of Siva-Brahma Parasakti, Jivatma, &c.
Brihadaranya (4.4.10; 6.1.2; 6.5.11) says that Vedas Itihasas Puranas &c. are the breathing of Brahma. Again Vayusamhita (I Part 1.24) says that Siva is the Author of 18 Vidyas. Upon this, if one contends and says that "Narayana alone existed not Brahma nor Siva," and He was the author of all Vedas, Puranas &c. (according to Subala Upanishat), we answer as follows. In certain Kalpa, Brahma was the creator of Vishnu, Rudra &c; in another Kalpa, Rudra created Vishnu Rudra &c; in another, Vishnu created Brahma, Rudra, creatures, Vidyas &c. (Vayu Samhita Part I.11). Beyond these three, was Siva Para-Brahma. Therefore what is mentioned in Subala-Upanishat belongs to the intermediate time of creation only.
It is further known from Maha-Bharata and Saiva-Purana that the meanings of Vedas should be expounded by the aid of Ithihasas and Puranas; Vayu-Samhita again says that Puranas construe the Vedic meanings with great effort, whereas the Saivagamas expound them with great perfectness. Therefore Upanishats, Puranas, and Sivagamas are respectively entitled to be called as sutras, annotations, and vast commentaries. As Vedas and Agamas stand in relation as Sutra and Bhashya, Vedas are called Samanya sruti and Agamas the special sruti in Maha-srokta.
The word Adhva (Katha 3.9) is expounded in Vayusamhita (Part 1.25, Part II, 15) as six Adhvas i.e. Mantra, Varna, Pada, Bhuvana, Tatva and Kala Adhvas. In Tatva-Adhava only, there are thirty six principles or Tatvas (which contain twenty four Atma Tatvas of Prasna (4.8), Seven Vidya Tatvas of Svetasvatara (1.2), and five Siva Tatvas of Brihat-Jabala (4.19)
Siva, Mahesvara, Rudra, Vishnu, Pitamaha, Samsara-Vaidya, Sarvajna, and Paramatma are the eight names of Siva; as He pervades all from Siva-Tatva to Earth (numbering thirty six Tatvas), He (Siva) is called Vishnu (Vayusamhita Part 1.28.36). Therefore the name Vishnu found in Rig-Veda (1.22.20) and in Katha (3.9) is only to be applied to Siva, and not to Narayana who pervades only twenty-four Atma Tatvas. The Dahara Akasa Upasana (திருச்சிற்றம்பல வுபாசனை) taught in the 8th Prapathaka of Chandogya is found in almost all the other Upanishats.
Uma, Haimavati (found in Kena) is the name of Parasakti of Siva only, who is neither Lakshmi of Narayana, nor the Amirvachaniya-maya-sakti of Ekanmavada. Kurma-Purana says that "Akasa" and "Vyoma" do mean the Parasakti of Siva. Therefore Gargi-Akasa of Brihadaranya, Akasa of Chandogya, and Vyoma of Taittriya &c. denote Parasakti (Svetasvatara 6.18) of Siva Brahma. By the reasons quoted above, we easily come to understand that all the principal Upanishats belong to Saivaism only, and those who worship the Vedic Siva according to the prescribed Saiva rules are called Vaidika Saivas. As Upanishats teach up to Jnana yoga (Vayusamhita Part 1.28,6) principal Upanishats treat of Path of Light, Brahmaloka (Sivaloka &c). The Jnana-Pada or Siddhanta, the essence of Upanishats is taught in Sarva Jnanottra, Devikalottara, Sivajnana-Bodha &c.
The whole Kailasa-samhita treats of Sivadvaita; this was taught by Subramanya to Rishi Vama-Deva, whose name is found in Aitareya 4.5, and Brihadaranya 3.4.10. The name Sivadvaita is seen in Kailasa-samhita 10, 96. Saiva Siddhanta was taught by Siva first to Vijnanakala, Pralayakala, Sanakas &c. The word Siddhanta is seen in Sivarahasya Khanda, Sambhava Khanda, 3.51. Siddhanta was also taught by Vayu to Rishis, and by Upamanyu, the son of Vyagrapada to Krishna, who taught Bhagavad Gita to Arjuna. The name of Siddhanta is found in Vayusamhita Part I.28.72. The word Saiva Siddhanta is found in Vayusamhita Part Ii. 24.177.
"Sa eva sarvagas sadbhir Brahma sabdena Sabditah" that Siva is called Brahma. Therefore Srikantha-Acharya is right in interpreting Brahma as Siva according to Srutis, Puranas and Agamas. Neither Meykandar nor Sivajnana-Munivar introduced either Sivadvaita or Siddhanta newly.