question about unlocking job

[Niwashi]

but having to level every class to 30? it 's a real pain.

Well, ones you're advancing you'll end up leveling to 50, then 60 and 70, and once the next expansion comes out, to 80. Level 30 is a milestone along the way where you can turn the class into a job that changes its style somewhat (more so for some than for others). There are other points at which they'll change nearly as much again because you get an important new skill, but the level 30 milestone is the one where they get another name as well. And the story being told in the class/job quests shifts into a new story arc at that point.