2.  The four worlds are the four fundamental levels of being or consciousness as considered in the Kabbalah:

Atziluth (nearness): the archetypal or divine world—Fire and the Spiritual Plane

Briah (creation): the archangelic world of eternal patterns of Platonic ideas—Water and the Mental Plane.

Yetzirah (formation): the angelic world of force and form—Air and the Astral Plane.

Assiah (action): the physical world of matter and energy—Earth and the Physical Plane.

In relation to the Tree of Life, the Four Worlds are presented in two different ways:

A. Four different levels on one Tree:

1.  
   1. Atziluth corresponds to the first through third sephiroth: Kether, Chokmah, and Binah.
   2. Briah corresponds to the fourth through sixth sephiroth: Chesed, Geburah, and Tiphareth.
   3. Yetzirah corresponds to the seventh through ninth sephiroth: Netzach, Hod, and Yesod.
   4. Assiah corresponds to the tenth sephirah: Malkuth.

B. Four different Trees one on top of the other so that Malkuth of the highest Tree is also Kether of the next Tree lower, and so on.

Meditation on both these ways will be meaningful.