Players who engage with a priest in the vast majority of RPG know they will have essentially a supporting role, and are therefore generally low refractory to spend their time helping others. WoW is no exception to the rule, the priest still probably the best class care and best support the game, but it is also far from being ridiculous in combat, including through some direct damage spells and DoT ( damage over a period) very powerful combined with excellent protection capabilities.
Firstly, the key point of course is a priest’s mana bar. To give an idea, I would say that his real life bar IS his mana bar as long as he is able to protect themselves (eg through the shield Divine Power Word: Shield) or cast spells recovery ( a lot of care as fast or Flash Heal spell recovery over a period as Renew), the priest would lose little or no energy. By cons, once the mana bar empty, low level armor makes it an easy target for enemies, and usually death occurs very quickly. Offensively, though still quite far from a pure Mage in damage and no variety of a Sorcerer spells are effective, especially when it comes to the damage of magic or sacred shadow magic.
The priest should focus on maximum points on the characteristics of intellect and spirit for mana, without neglecting the stamina, and then choose your clothes accordingly.