The gnostic tradition emphasized knowledge (jñāna) and used Skt. as its medium of expression. Its dualist theology is summarized in the Tattvaprakāśa (Light on the Tattvas) of Bhojadeva (c.11th cent.) and expounded in Aghorasiva's commentaries on dualist Āgamas.
The devotional tradition, which used Tamil as a medium of expression, emphasized bhakti and surrender to the Lord Śiva. It revered the twenty-eight dualist Āgamas, but equally important if not more so was the devotional Tamil poetry of the Nāyaṇmārs (4th–9th cents. CE).
The most important theological text of the school is the Tamil Civañāṉapotam (Skt., Śivajñānabodha) by Meykaṇṭatēvar (Skt., Meykaṇḍadeva) (c.1220 CE) which is said to be the quintessence of the Vedas and Āgamas.
"Śaiva Siddhānta." The Concise Oxford Dictionary of World Religions. . Encyclopedia.com. (October 19, 2018). http://www.encyclopedia.com/religion/dictionaries-thesauruses-pictures-and-press-releases/saiva-siddhanta
"Śaiva Siddhānta." The Concise Oxford Dictionary of World Religions. . Retrieved October 19, 2018 from Encyclopedia.com: http://www.encyclopedia.com/religion/dictionaries-thesauruses-pictures-and-press-releases/saiva-siddhanta