The brahmin differs from every conferrable office in this atlas in that membership is by birth, and in the traditional view nothing can grant it and nothing can remove it.
Birth and the sacred thread
Ritual eligibility follows from birth and from the upanayana, the initiation with the sacred thread, after which a man is dvija, twice-born, and eligible to study the Veda and to perform rites reserved to him. Not all brahmins are priests, the varna has supplied scholars, administrators and landholders, but the priestly function is reserved to it in the classical scheme, and temple priesthood in most large Hindu temples remains restricted to particular brahmin communities.
Contested, and litigated
The restriction is contested and has been challenged in law. Temple-entry movements from the 1920s, the abolition of untouchability in the Indian constitution, and state legislation in Tamil Nadu and Kerala permitting priests from any caste have all pushed against it; the Supreme Court has held that appointment cannot be restricted by caste but that a priest must be trained in the relevant agamic tradition, and temples have continued to resist in practice. Anti-caste critique, and that of Ambedkar in particular, treats the brahmin ritual monopoly as the foundation of the caste system rather than an incident of it, and an account of this office that leaves that out is not describing it honestly.