While explaining why a sudra is not entitled to philosophical wisdom, Sankar writes (on Brahma sutra i.3.34):
The sudras have no such claim, on account of their not studying the Veda. A person who has studied the Veda and understood its sense is indeed qualified for Vedic matters. But a sudra does not study the Veda for such study demands as its antecedent the upamayana ceremony [i.e. the inititation ritual conferring on one the status of dvija] and that ceremony belongs to the three higher castes only.
Further to this, note what Manu (whom Adi Sankar is pleased to quote frequently in his writings) says (Manu Smriti x.4):
The Brahmin, the Ksatriya, and the Vaisya castes are the twice-born ones(dvijas). But the fourth, the Sudra, has one birth only. There is no fifth caste.
It is of course well known that added to their first birth in the mother's womb, the Brahmins, Ksatriyas, and Vaisyas are supposed to have a second birth derived from the upanayana or inititation ritual. The Aitareya Brahmana (i.3) gives a vivid description of this mimatic rebirth. As explained in the Aitareya Brahmana, the upanayana or initiation ritual is intended to introduce the individual to the full status of the priviliged class of people to whom is permitted this ceremony, the general descriptive epithet of which is accordingly the dvija or twice-born. The initiation rite or upanayana being forbidden for the sudra, he has only one birth and is hence without the rights and priviliges of the dvija.
Recommend