A philosophical system of thought that accepts the authority of the Vedas is called Astika. Certain other philosophical systems that openly question and reject the validity of the Vedas are known as Nastikas. It is believed that Siva advised Skanda to be born as a human being while He would incarnate as Adi Sankara to revive the spiritual and ethical heritage of the Vedas at a time when non-believers were reigning supreme, said Sri K. Ramamurthy in a lecture.
Skanda was born as Kumarila whose regard for Vedic tenets was very high and, being a Mimamsa scholar, he championed the Karma Kanda of the Vedas that advised performance of rituals according to scriptures. Kumarila encountered and challenged the prevailing philosophical debates to establish the supremacy of the Vedas. But his opponents were not satisfied by his convincing arguments and he was subjected to severe tests to prove his faith.
He was asked to fall from a precipice, a feat that none would dare considering the confirmed risk to life this challenge posed. But with faith in the Vedas, Kumarila succeeded and fell on the earth from that height as would a flower unhurt and unscathed. Another challenge was that he should guess the contents placed inside a pot. The challengers knew it was a snake but Kumarila said it was Vishnu on His Adisesha. It turned out that Kumarila had spoken the truth.
Around the same time Siva was born as Adi Sankara and details of his life and times are recorded in Sankara Vijaya. As a devoted son, he took care of his mother with love and reverence. It is said that he requested the Poorna river to change its course to flow near the backyard in his village house to enable his mother to have her ablutions. When he took up sanyasa, he promised to perform the final rites for his mother.
He composed Manisha Panchagam in Varanasi when Siva came in the guise of a hunter belonging to an outcaste community to inculcate the practice of the truth of Advaita and not merely dwell in the theoretical concepts. Adi Sankara brought about an awareness of the purpose of existence of the Jivatma in a very marked manner.