The Priestly source (or simply P) is perhaps the most widely recognized source underlying the Torah. It is both stylistically and theologically distinct from other material in the Torah, and includes a set of claims that are contradicted by non-Priestly passages and therefore uniquely characteristic: no sacrifice before the institution is ordained by Yahweh (God) at Sinai, the exalted status of Aaron and the priesthood, and the use of the divine title El Shaddai before God reveals his name to Moses, to name a few. In general, the Priestly work is concerned with priestly matters – ritual law, the origins of shrines and rituals, and genealogies – all expressed in a formal, repetitive style. It stresses the rules and rituals of worship, and the crucial role of priests, expanding considerably on the role given to Aaron (all Levites are priests, but according to P only the descendants of Aaron were to be allowed to officiate in the inner sanctuary).