The cleric casts spells from the cleric spell list and has limited access to 2 domains spell lists.
The cleric casts spells from the cleric spell list and the druid spell list, and the ranger spell list, and the paladin spell list, and the adept spell list, and the Blackguard spell list, and each and each and every domain spell list, (without the 1 per level per day limit of the cleric has) and every new prestige or base classes spell list that gets added to the campaign, and all at the lowest levels that anyone gets them at. some prestige classes are balanced getting spells at a lower level than any base class could because by the time members of these classes get them they are of appropriate character level to use the spell, the archivist short circuts this logic.