The effect of raise spells is to revive a player who has been KO'ed. When a player is brought back from KO, they will regain some of their lost experience points; however, they will temporarily have weakness status. This cannot be removed by any means aside from waiting for its full duration.
A subset of raise spells, "Reraise" spells grant a buff to the caster which automatically bestows a raise effect on them if they are KO'ed.
"Raise" spells are single target spells which will bring a target back from KO with weakness status (reduced attack speed, increased recast timers, reduced maximum HP and MP). A raise spell can be cast on any target whether in the user's party or not. Raise, Raise II, and Raise III each cost 150 MP to cast; however, the EXP and HP restored increase with the higher tier spells unless the target is below level 50, in which case the EXP and HP restored will be equal to that of Raise.
Arise is a powerful raise spell unique to White Mage that revives targets with a reduced weakness duration and full HP (which allows raising in tricky blood aggro situations), and additionally grants the target the effect of Reraise III upon revival.
"Reraise" spells are self-cast spells which will bestow a Reraise effect on the caster. This effect lasts 60 minutes. If the caster is KO'ed while this status is in effect, they will automatically receive a raise effect equal to the tier of the Reraise spell cast (see table above; Reraise IV is equivalent to Arise).