This is a dropped spell from a recent Paizo twitch stream. Thought the community here might want to see and comment if they haven't already.
This is what used to be flame strike, I would guess.
I'm a fan of this rework of flamestrike. AoE Holy Fire or Holy Spirit damage with a DoT can proc quite a few weaknesses and ignore a common resistance when it shows up. Seems reliable, and heightens pretty well, asuuming your GM doesn't roll well on those persistent checks often.
Looking at the success effect (without persistent damage) it feels like an overpriced fireball at 5th level. You'd want roughly 5d6 worth of blast on success, not 3d6, I don't know how relevant/powerful spirit damage will be though, not like the divine list is know for it's good blast so it might see play regardless due to that
I'm guessing the damage is lower due to the persistent damage and the fact that spirit damage can take effect if the target has fire resistance/immunity.
"Spirit damage" would be the substitute for positive damage, maybe? I don't remember that being a damage type.
I believe that is the substitute for alignment damage.
Spirit damage is a new damage type that replaces the law/chaos alignment damage. There was also a leaked sidebar from Rage of Elements which has the following:
Vitality and void replace positive and negative traits and damage.
I presume this is due to positive/negative being OGL terms.