Kabbalistic cosmology describes creation unfolding through four sequential "worlds" (olamot), each representing a further step of divine light's concealment and condensation as it moves from pure, unified spirit toward physical matter. The concept first appears distinguished in this specific four-part form in the small work Masseket Atzilut; it reaches its mature, fully developed form in Lurianic Kabbalah, where each World is also described as containing a complete Tree of Life of its own β meaning there are, in the fullest reading, forty sefirot rather than ten, one full set nested within each World.