I think it's because these concepts are universal archetypes. The world is really all described through metaphor, and the supreme ideas just as much as the lowly ideas. Apparently the Kabbalah existed far prior to the making of the Old testament, and I feel like during that time, there must have been a more intimate spiritual connection between east and west. The system is made to help us see the connections between things and evolve our awareness of the universe. The same way that there are countless yoga's of the east, all supposedly leading to enlightenment, Kabbalah and the other systems of Crowley do the very same. I cannot say it is the best system though, but it is definitely one of the most rewarding. Crowley's path can be described as a left-hand path as opposed to a right-hand path.