People not familiar with how the different roles operate may mistake priests for clerics and vice-versa. But they do not function in the same way and they have different tasks to perform within their churches. For the most part they have less in common than the average person might think.
Clerics perform the same in every corner of Partum with some minor differences here and there. For instance Slothjemian clerics have access to the Weather sphere but not the Astral sphere. Forkanzan clerics cannot cast above the 5th spell level. Across the board though clerics operate pretty much as paladins do in how they maintain their personal relationships. They are both expected to remain chaste until marriage in which case they can of course engage in marital bliss.
Priests however are not so lucky, and must be both chaste and celibate. Unlike clerics who can gird themselves up in whatever armor they choose priests suffer a lot of the same restrictions as do wizards. Furthermore they have a somewhat more limited access to spells depending on what they have focused on theologically. Some priests are devoted to healing and might have tremendous powers in that regard that don’t rely on spells at all. Others are committed to combatting the undead and have additional abilities that clerics will never have. Priests are also not as limited in their choice of weapons. Depending on their focus they can wield all manner of different destructive implements. Priests are also necessary for certain key religious services that are rarely given to clerics to perform.
The other major difference between priests and clerics in Partum is their ability to climb the power structures of their church organizations. Priests are always able to gain promotion by virtue of their devotion to specific duties required of them by their superiors. Clerics rarely are able to gain such promotions because they are out and about actively fighting evil and don’t set aside time for paperwork and pleasantries. Clerics that manage to become bishops are incredibly rare. Virtually every executive within a church hierarchy is going to be a priest instead of a cleric. In exchange for having a family they gain surprising amounts of power and wealth. Not really all that much of a sacrifice…