[Endoperez]

So you can make researchable pure-Holy spells? If so, you have to decide a school, and that affects which nations get to use what priest spells. Why not put a holy spell at each school's levels 4 and 7, or something similar? (3/5 and 7 for construction)

Conjuration:
4 - better Banishment, H2?
7 - a battlefield summon spell for one or few weak creatures/spirits, perhaps 1 per Holy level? perhaps something on Ghost Wolf power level?

Alteration:
4 - better Bless: bless + buff (perhaps luck), self only, H1
7 - unit buff, H2 Legions of Steel, +4 strength or something

Evocation:
4 - H2 damage spell similar in power to a Bolt spell, but not elemental damage (no immunity)
7 - AoE 1 or AoE 1+ damage spell, H2, again non-elemental

Construction:
3 - ???
7 - Summon a sacred Watcher-like construct with gold upkeep. Ranged attack that deals extra damage against demons. or something better. Pity there aren't any Holy items.

Enchantment:
4 - H1 heal spell, nr of effects scales with Holy
7 - banish or control magic being, H2-3

Thaumaturgy:
4 - H3 Panic/Terror-style spell
7 - high-dmg Mind Burn at enemy sacreds only

Blood:
4 - H3 Curse + Horror Mark + Decay + (resistable) stun
7 - H1-2 spell that causes affliction