In order to make Spirits fit in the general rules for comparison to things such as Disciplines, Gifts, Spheres, Arcanos, etc. Spirits of power levels 1-10 are 1’s, 11-20 are 2’s, 21-30 are 3’s, 31-40 are 4’s, 41-50 are 5’s, 51-60 are 6’s. This places spirits amongst the same categories as PC’s in terms of comparing things like their charms etc, to be resisted and countered. 

In other words if a being is attempting to fool, cajole, use a supernatural power on a spirit, it compares its power level to the discipline, rank, sphere, numina, Arcanos, cantrip level of the pc to see if it is affected. If the spirit power level is lower, it can’t even check for the Obfuscated Vampire, equal means it may attempt to check with the correct abilities, higher means the Spirit is unaffected. This only goes for Spirits that use power, not Wraiths.