White Mage is the second healer job you can acquire in this game, although normally it's the first. It has good stats for healing purposes, but generally mediocre stats otherwise. It's nice for nostalgia purposes, but frankly, the Bishop job makes it largely unnecessary.
In the previous game, White Mage was a staple up to mid-game because of its reliable healing powers. Here, it appears awkwardly near the middle of the the game, at a time where the Bishop is starting to free itself from its underpowered shackles. They have some nice abilities though.
Specialty: Angelic Ward
The user has a 50% chance of halving damage from any attack. Does not trigger for poison or freeze damage and has no effect when triggered against certain abilities.
This is a better Specialty than the White Mage's old Silence Immunity. Since you need to rely on White Mages, who are rather fragile, it's good that they've got a semi-reliable way of surviving hits.
Level 1: White Magic Level 1
Cure restores a small amount of HP, while Aero deals weak wind damage. These spells can be cast on a group, but their power will be reduced. If you grabbed the Red Mage job, none of this should be new. Either way, these spells are too weak right now, so simply learn them and carry on.
Level 2: Angelic Ward
That was fast. Now you can give this to a Bishop or other character that you really don't want KO'd. Works well with tank-types too.
Level 3: White Magic Level 2
Esuna cures all ailments and Raise revives KO'd characters. Back then, these spells put the Red Mage ahead of Bishops, but by now the Bishop has already learned equivalent spells. Nonetheless, they're useful spells to have.
Level 4: White Magic Level 3
|Command||Cura: 20 MP Aerora: 25 MP|
Stronger versions of Cure and Aero respectively. Ignoring Good Measure, Cura heals almost twice the amount of HP as Vivify at the time you acquire White Mage. So if you want optimal healing, you may want to momentarily jump ship to White Mage.
Aerora is a nice improvement and far stronger than the Wizard's Spirit Magic. However, during difficult battles, your White Mage will probably be healing overtime, so it's not really useful for them. A Wizard on the other hand...
Level 5: White Magic Level 4
|Command||Curada: 30 MP Esunaga: 36 MP|
Curada is an even stronger version of Cure and Esunaga cures the party of ailments. Right now, you've caught up with the Red Mage and left the Bishop in the dust.
For a while, nothing will beat Curada in terms of healing power, especially when it heals close to half of your party's HP. Once you acquire Benediction, the two spells will be evenly matched, but eventually Curada will fall behind as your party's HP increases.
Level 6: Silence Immunity
The one thing (besides death) that healers (and mages) want to avoid most is silence. Of course, you can equip a White Cape to do the same thing, but perhaps you want to save the accessory slot for something else?
Level 7: White Magic Level 5
|Command||Curaga: 40 MP Aeroga: 45 MP|
Curaga is the White Mage's best healing spell, while Aeroga is its second-best offensive spell. The scrolls for these spells are acquired late in the game, so chances are you've probably gone back to using Bishop in the meantime.
When you do get Curaga, it's initially worth using since it heals more than a single Benediction. However, after a dozen levels or so, Benediction becomes better again due to the unfortunate fact that HP increases at a faster rate than Mind.
Level 8: Group-Cast Master
This is the main reason to train a White Mage, but ironically the reason to dump it. Spells that originally suffered a penalty when group-cast no longer have this penalty. Great for White Mages, right? Sure, if Benediction didn't exist. Say "hello" to 100% HP recovery for all your party members!
Level 9: White Magic Level 6
|Command||Arise: 50 MP Holy: 80 MP|
Arise revives a character with full HP, while Holy deals destructive light-based damage to one. Sadly, it's too little, too late. Bishops already have access to Resurrect far earlier, while Holy is nice, but better in the hands of a Wizard or other offensive spell-caster.
Level 10: Circle of Life
If you need a safety net, this is one of the best ones. Just keep in mind that the user doesn't get revived.
Level 11: White Magic Level 7
Raise All revives all party members with full health. It also cannot be reflected. A fantastic spell any way you look at it, but not worth assigning White Mage as a primary or even secondary job.
It's a bit pricey, but you can use the Black Mage's Group-Cast All or Mist/Blast Spellcraft to make Resurrect do the same thing. Or try not to die in the first place!