The Rule of three is closely related to Karma. In Karmic beliefs, the basic idea is, “You reap what you sew.” Many faiths have adopted this spiritual check and balance system, but have added another element to it. The rule of three states that what you send out will return to you three fold (Times Three). This is an interesting principal to uphold because it is not a specific deity punishing its worshippers, but the practitioner themselves. It is their choice to send blessings, or curses out to the world. In return, that person will either be rewarded or punished by their own actions.
Below are a few links that explain the Rule of Three within different faiths even Christianity. Enjoy! Love and light to all!
Pagan in General:
Love and Light to all!