The Four Worlds are widely correlated with the four letters of the Tetragrammaton, the four letter Hebrew name of God, and Atziluth, the highest, is assigned the first letter, Yod, read in this scheme as the point of origin, undifferentiated and prior to any extension into form. The correspondence gives the cosmology a second structure layered onto the first: not only four descending worlds but four letters of a single name, each world a further unfolding of what the letter before it contains.
Kabbalistic teaching also holds that each of the Four Worlds contains a complete Tree of Life within it, ten sefirot repeated at every level, so that Atziluth is not simply the topmost world but a whole tree in its own right, its own crown, wisdom and understanding folding downward into the world of Beriah below, which in turn contains its own complete tree. This fractal image, worlds within worlds each holding the same structure, is sometimes described as a ladder, ascended in meditation or descended in the account of creation.
Atziluth corresponds in the soul scheme to Chayah, or in some formulations to Yechidah, the highest levels of the soul, placing the human being's own subtlest aspect at the same rung of the ladder as the world nearest the divine name's first letter.