Does not confer damage immunity. Rather, it creates a "+100% damage resistance" modifier against enemy attacks and friendly fire damage, which in turn can be reduced by other effects or properties, notably the 50% reduction in effectiveness inherent in all spirit-element attacks. Thus, this only reduces the friendly fire damage from a spell like Walking Bomb by 50%, which in this example still leaves the warrior exposed to an exceedingly-high amount of damage.
Combining this spell with other damage reducing abilities such as Stonewall or Bulwark will not increase damage resistance any further, as the property caps at 100%. Although most forms of damage can be prevented by hitting this mark, spirit element attacks will cut this 100% in half, thus ensuring the element will maintain at least 50% of its true damage without specifically wielding spirit resistance.