Still basing my analysis mainly on Talcott Parson's introduction, I come to Weber's initial topic: primitive religion.
According to Weber, all human society possesses what sociologists would classify as 'religion,' being inter alia "conceptions of a supernatural order, of spirits, gods or impersonal forces which are different from and in some sense superior to those forces conceived as governing ordinary "natural" events...." It's mentioned in particular that work by anthropologists has confirmed that the belief in the supernatural is universal.
Weber is particularly interested in distinguishing between primitive and sophisticated forms. Parsons explains by making the distinction between "natural man," a man belonging to primitive history, and rational man, of more recent times (note the absence of quotes) - it's insisted that for the former "cultural baggage" exists, and only the latter has the level of consciousness to consider dispensing with it. Or is it's removal in practice more of an orphaning of or divorce from practices that contain relevant spiritual meaning?
Continuing the distinction, for Weber breakthroughs [from primitive religion] is an important topic, searching for the directions they take and so on. From what to what? He uses the method of binary differentiation related respectively to and within the spheres 'material'(utilitarian-oriented, associated with daily living) and 'ideal' (to do with meanings and conceptions of the supernatural and the experiential dimension). The binary approach is applied repeatedly to gradually draw out finer distinctions. The outcomes of binary decisions impact change: either evolutionary changes in established order or consolidation of the established order [and institutionalisation]. It's subsequently reiterated that the primary interest for Weber is religion as a source of the dynamics of social change, not stability, and I take it is looking for conditions for processes of change with breakthrough.
A key dichotomy is expressed in terms of the functions of magician vs priest as mediators between humans and the supernatural: the former's ad hoc use of formulas vs the more systematic 'cult' that uses ritual and worshipping agents. Around this is the development of conceptions of the supernatural ... and hence relationships, claims, obligations etc. (using intermediaries). Note that for him the existence of the supernatural doesn't imply transcendental goals, especially not for primitive society.
Their functions are distinguished especially by their handling of another fundamental dichotomoy - between ethics and taboo: priests are concerned more general and universal orientation, and pattern of actions, whereas magicians deal with specific prescription and proscription of actions.
A footnote to this post: the dispensing with cultural baggage has been quite topical in Western Buddhist circles - some want to detach themselves from what they perceive as unnecessary cultural trappings, particularly the rituals, which come from e.g. the Far East - so as to live the 'pure' and 'pristine' teachings of the Lord Buddha. This might in Weber's perspective be a reflection of sophisticated culture - indeed the removal of attachment to rituals would remove one of the lower samyojanas binding to the 'lower shore' of samsara, but that's a really advanced state of practice...