Mages specialize in the casting of spells, offensive ones in particular. Mages have the highest-powered magic of any class, and are the only classes able to use the draconian and enchanting spell groups. They are also very skilled at the use of magical items, though their combat skills are the weakest of any class.
Clerics are the most defensively orientated of all the classes.
Most of their spells focus on healing or defending the faithful, with their few combat spells being far less powerful than those of mages. However, clerics are the best class by far at healing magics, and they possess and impressive area of protection magics, as well as fair combat prowess. Thieves are a marginal class. They do few things better than any other class, but have the widest range of skills available. Thieves are specialists at thievery and covert actions, being capable of entering areas undetected where more powerful adventurers would fear to tread.