SORCERERS - These are the pioneers, the genii, who do things in ways they themselves cannot really explain. They are the ones who first harness the basic “forces” inherent to the system. It all seems obvious and instinctive to them, but few others actually grasp what they are doing. Usually misunderstood and if their book has no obvious use, mocked.
WIZARDS - The first who understand sorcerers - they take the work of the pioneers are go "I can do this" or "oh, I get it" and break it down into parts, make it reliable, understandable and useable by others (well, other wizards at least). Using this knowledge they begin to build systems and functions from the ground up. Pioneers in that they take an otherwise useless function and make it relevant.
SHAMANS - Whether by chance or design, these people will look at the functions built by wizards - and enhance them. While they themselves do not fully understand how the functions work, they know what each function does, and how to use and link them together. They can tell when a function is corrupt, sometimes where its corrupt and also how to fix it. Note that they do not know how to build a function from the ground up - but can repair, restore or combine functions by comparing it with another. They are key in translating the operation of functions into certain methodologies for "communication"
PRIESTS - They popularize the functions. At this point, the priests have little to no knowledge of the underlying functions - just the methodologies involved. They are really good at identifying, simplifying and spreading use of these methodologies though. Cannot repair, let alone create functions, unless aided by an existing function designed to do so in the first place. Cannot create their own methodologies.
SOLDIERS- The end result. They take the Holy Sword of +2 and swing. Five hundred thousand of them can take down a dragon. And possibly do other important stuff, like banking.