Intelligence
Intelligence increases damage and healing from spells. The more the better. There is no known cap to the benefit.
Perception
Perception decreases an enemy target's ability to resist a spell cast by the Mage. This is a very important stat for a Mage, as they need to be able to penetrate a target's magical resistance or they are essentially useless.
Wisdom
Mages consume a lot of mana to dish out their damage. Wisdom increases a Mage's mana pool and mana regeneration rate.
Luck
Luck determines critical hit chance vs. glancing blows. Glancing blows are the opposite of critical hits; they are critical failures. The lower a Mage's luck, the more erratic their damage will be as they will have a higher chance of a "glancing blow" heal which does little damage. For Mages, Luck should be kept on par with Intelligence.
Agility
While not an obvious stat for a Mage (or other magic classes), Agility affects the chance of dodging an enemy's physical attacks. It comes with most Mage gear and is useful for survivability.
Endurance
Endurance reduces the chance a Mage will be hit with a critical hit.
Stamina
Stamina increases a Mage's health pool.
Conviction
Conviction effects a Mage's control spells, both duration and chance to hit.
TIP: Willpower increases a character's chance at resisting control effects.
Faith
From the Healer's guide:
Faith determines a healer's ability to penetrate wounds. Wounds are accrued during combat and the more wounds a character has, the less effective healing will be on them. A higher faith will allow a healer to penetrate wound complexity and have more effective heals.Quoted here since Mages do have a single healing spell.
