Similar to how Arcana is broken up into various schools, Theurgy is broken up into separate Domains. The use of Theurgy is accessing one of these Domains and drawing power from it to change reality in a manner very similar to common magic. Each Divine has a set number of Domains they have access to, and each Domain can have several Divines that can access them. It is a common belief that a Domain shared by multiple Divine is far stronger than those only accessed by only a single Divine.
Domains naturally have a singular focus and can only alter the world when manipulating their Domain's core concepts. The "Fire Domain," for instance, would only affect flames, heat, or similar concepts. Because of this, Divines are only able to use their immense power to alter their particular sphere of influence. For this reason, a Divine of Flames cannot use Theurgy to bring about a flood. However, whatever skills a Divine had during their brief mortality, they also retain during their Divinehood. Such as a Magi who focused on Conjuration may still have the ability to conjure things from nothing. However, they cannot rely upon Theurgy as they remain restrained to the natural limitations of Arcana.