Type: Summoning
Strategy: This spell is like animal summoning I, except that the creatures are more powerful. Still, this doesn't summon a creature worth your time, so wait for animal summoning III.
Importance: Low
Type: Touch damage
Strategy: Much like cause serious wounds, this spell is a touch damage spell that will do 27 points of damage. Like its earlier incarnation, touch damage spells are abysmal for mages, but they serve to boost the already competent fighting abilities of the priest. For these spells, you must wait until you are attacking an enemy worth casting this spell on. Then, once you are out of harm's way, and the target is concentrating on attacking another party member, cast this spell. Once cast, you have two rounds to successfully hit the enemy. Once you do, this spell will deal 27 points of damage to it with no saving throw. If you don't hit it, though, the spell will be wasted. So, make sure your priest has a good enough weapon, and you are in a position to hit. All in all, if used correctly, cause critical wounds, like the rest of the line of priest touch spells, is extraordinary.
Importance: High
Type: Defense
Strategy: Granting immunity to spells like charm, domination, command, sleep, and confusion, chaotic commands the protection form of free action. Instead of curing, it prevents. However, like many armor spells, it only affects one creature. For everyday party use, that simply isn't good enough. If you find yourself under duress, though, casting this on your main spellcaster will ensure that he is unaffected, so he can proceed to cure the rest of the party with free action.
Importance: Moderate
Type: Cure, heal
Strategy: Cast on a hurt party member, this spell heals 27 points of damage. For Baldur's Gate II, that amount is decent and can be used outside of combat to heal the party back to full strength. If needed, cure critical wounds can even serve as a backup in-battle heal. Also, the spell is useful to cut down on hours of rest, so if you find no other spells, fill up level 5 with it.
Importance: High
Type: Imbuement
Strategy: An upgrade to holy power, this spell gives the caster 18/00 strength and a large bonus to THAC0. However, unlike holy power, which helps your priest act a bit more like a fighter, this spell will disable spellcasting for the length of the spell. In essence, champion's strength kills your priest's abilities and is much worse than its lower-level equivalent. Stick with holy power.
Importance: None
Type: Damage
Strategy: One of the crowning priest damage spells, flame strike will deal 1d8 damage per level. Even if it is resisted, it will still deal half damage. At higher levels, flame strike will do upward of 50 points of damage and packs a serious punch. Always keep this spell memorized and always use it as one of your main damage spells.
Importance: Vital
Type: Hindrance
Strategy: Identical to the level 1 spell command, this spell will incapacitate the target. However, greater command will incapacitate the target for one round per level of the caster. At higher levels, this will serve to take a creature out of combat completely. However, the spell is often resisted, so make sure to lower the target's magic resistance before casting it.
Importance: High
Type: Damage, hindrance - druid only
Strategy: Like its level 3 cousin, insect plague is rather an all-in-one spell. Now, this spell also confers a 100 percent spell failure rate on the target. Also, it has a chance of instilling fear in your enemies. Lastly, though the damage is still negligible at one point every two seconds, all the other effects add up to make this a good spell. However, the spell will also become resisted quickly. So, use it while it lasts, then move on.
Importance: Moderate
Type: Defense - druid only
Strategy: Much like the wizard spell stoneskin, iron skin completely protects the priest from a number of normal physical attacks. With more skins (number of resisted attacks) gained with each level, this spell's importance is obvious. If your party is jumped, and it will be, having your party well defended is important. So, this spell should be on at all time while adventuring. With a duration of 12 hours, this spell can last between rests.
Importance: Vital