Wisdom is one of the six character abilities. It's very important for clerics and druids, as a high wisdom grants extra spell slots per level. They also have a higher minimal number for this character ability. Rangers and paladins also have high amount of wisdom as a minimal requirement, but do not gain any bonus spells from having a high wisdom - their spell slots are determined solely by their level.
The Bonus spells are cumulative, a cleric with 15 wisdom has two level 1 spellslots and one level 2 spellslot as a bonus for example. For non-caster classes, intelligence and wisdom only adds a bonus to lore bonus, so it's wiser to spend points on the other character abilities when creating a character.
Scores table Icewind DaleEdit
Bonus Spellslots (Cleric, Druid)