I'll make a list for each skill
1. Maple Hero - Stats Enhancement
Definitely worth a few points, every 2 points in it raises the %.
2. Quantum Explosion - Charging
Strongest attack next to genesis, worth even the 1st point as it's still stronger (and 35% mastery isn't that bad for the 1st point). It's a lot cheaper than genesis too.
3. Mana Reflection - Reflect Damage
Mandatory point, even if you only put 1. It only lasts for 10 sec. but it reflects 55% already; the 26 mp cost is negligible at 120+ and even if it doesn't reflect 55% damage it still saves you from 55%.
4. Infinity - Infinite Mana
Not really sure. The cooldown never goes down, only the duration increases. I'd put 1 point in for fun, but I don't know how it'd fit in a build
5. Holy Shield - Status guard
Same thing as infinity - no idea, 1 point for fun. It looks rather useless in the long run though as the only new stat gets its own skill to cancel it out (madness).
6. Angel Ray - long range single target holy spell
Another HA reject, useless in my opinion compared to all the other skills.
7. Bahamut - holy dragon
I'd max this early on, maybe the 2nd thing I'd max, at least 3rd. It's powerful, mobile, and doesn't use a summoning rock, what more do you want ?
8. Genesis - long range multiple targets holy spell
I think this speaks for itself.
9. Resurrection - Revive dead ally
At least 1 point so you can do it at all. The cooldown is basically an hour (well, 57 min.) but on most boss runs (the only place this is useful) there's more than 1 priest.