Warriors are the masters of weaponry. They have the most potential of all the professions to deal devastating physical damage in a melee. They are masters of swordplay, and can use their weapon to parry or disarm their opponents. Also, they can repair weapons and armor that have been damaged, and they can make weapons more effective by sharpening them. Warriors have the ability to bash their opponents, making them temporarily unable to flee.
Warriors lack the potential to deal good damage with spells.
Clerics are the masters of the art of healing and protection. They can heal others much quicker and better than any other profession, and they can soften opponents blows through the sanctuary and stone skin spells. They can cast spells that harm creatures and players of an opposing alignment, and they can deal out large amounts of damage to undead creatures. Clerics don't have the potential to deal as much damage with either weapons or spells as the other professions. Thieves are the masters of the art of poisons.