Some spells are targeted, like this one, and require a ranged attack to hit. That determines the success of the spell. Others automatically hit and are then contested. That's when your CHA comes into play, as a higher CHA helps to overcome the target's resistance.<br/><br/>Of course, I may be inserting my 3.5 / Pathfinder rules mechanics into things, so let me know if that appears to be the case!