Barrier grants the target elemental resistances. They are granted in order, based on the number of successes, to a maximum of seven resistances. They are cumulative, but do not stack. The resistances granted are as follows: 1 Success: Matter 2 Successes: Fire 3 Successes: Mind 4 Successes: Lightning 5 Successes: Death 6 Successes: Poison 7 Successes: Body
The Spell was probably intended to grant resistance to Ice for 8 or more successes, but it does not. It generally isn't all that useful because you have to spend so much time leveling it up. Note that the in-game messages about resistances granted by Barrier are incorrect.