Who is The Masters from Many Lives, Many Masters and what is their importance?

It is difficult to pinpoint exactly how many Masters there are. There appear to be two. Occasionally, others described as "guardians" speak. The Masters are entities who channel through Catherine when she is in the in-between lives state. Catherine's voice is said to become huskier when they speak through her. It is by these sound variations that Weiss recognizes who is speaking or conveying. The Masters convey knowledge and wisdom regarding the seven planes the soul must evolve through in order to achieve "wholeness." They compare physical state to school where lessons are learned. The Masters primary message is that as long as lessons of charity, kindness, faith, and love are not learned. the soul is doomed to return to physical form until it learns to be good toward its fellow man. One of the Masters is described as The Poet Master. He conveys much philosophy and wisdom. The other is the Master Spirit. These messages are meant for Weiss, who is destined to eradicate a variety of fears from his patients in the same way his is doing for Catherine. Freeing fears of death from the psyche and proving the soul never dies is the proper way to cure the soul and to evolve faster to achieve its rightful place with God.