Resurrection is a skill in the Heavenly Light skill tree of the Mage class.
Skill Description: Resurrect the dead player for 10% with recovering his/her HP and MP by the rescue pray.
Required job: First job
Required points: 5 points in Heavenly Light
Is requirement for: Party Resurrect
Skill type: Support Skill
Attribute: Light
Cool time: 8 seconds
MP Usage: 15 MP
Target: Any Player

Fairly obvious what it does, less obvious that it's of very little use, due to the fact that there are scrolls which do exactly the same thing which don't cost that much. For an FS needing every point they can get, it's probably better not to get this and ask your party to get scrolls instead.