The great whore is the lower nature that has sold itself to the senses, the desire-self that gives its energy to whatever offers pleasure, and she sits upon many waters because she rules the restless multitude of thoughts and feelings that surge through a person. The number 7 belongs to the completed cycle of the inner centers, so the 7 angels with their 7 vials are the full order of higher forces come to weigh and expose her.
Judgment here is the seeing-through of that scattered, self-selling nature. The desire-self that drinks from every passing appetite is finally recognized for what it is and its rule over the inner waters ends.
Great whore: the lower desire-nature that sells its energy to the senses for pleasure
Many waters: the restless crowd of thoughts and feelings the desire-self rules over
7 vials: the completed set of higher powers poured out to expose and weigh the lower nature
7 angels: the full order of the inner centers arrayed to bring the desire-self to judgment