You meld the arcane energies of the world to surround your target with a protective magical force surrounds it until the spell ends. The target's AC is improved by your spell casting ability modifier (Intelligence for wizards, Charisma for sorcerers) . This spell will last a minute and fade after the duration expires. 

This spell will stack with armor. The spell shatters and ends if the target is hit with a ranged weapons attack, melee weapon attack or magical attack by rolling the amount of or higher than the total armor class. 

Example, a warrior wearing armor and using a shield has an armor class of 18 without the spell.  With the spell that warrior has an armor class of 21 (due to a nifty +3 Intelligence modifier from the kindly wizard who cast it). When a foe hits with either a ranged weapon attack, melee weapon attack, or spell that uses an attack roll to hit, and the total roll is 21 or higher, the spell shatters and ends.