The four worlds give Kabbalah a graded model of reality, from the most subtle and divine to the most dense and material, down which creation descends and up which the soul and the mystic may ascend. The Golden Dawn used the four worlds, with their Trees and colour scales, as a key part of its system of correspondences.
The atlas gives each world its rank, its inhabitants, and its correspondences. The sephiroth repeated in each world, and the parts of the soul correlated with them, are treated in their own categories under Kabbalah & the Tree of Life.