There is always a part where your party is nearly dead, that's when you need a white mage.
The White Mage has 3500 hp and 5000 mp
Cure: +500 health, cost 100 mp
Curaga: +1500 health, cost 950 mp
Blind: blinds enemy(the enemy cannot attack next turn, can use an item or heal, just can't attack), costs 400 mp
Shell: 1/2 damage to next attack dealt to the ally.
Angelic Presence: All allies get shell, all allies get healed +1000 hp and all status effects are healed, costs 1500 mp