The Four Worlds are widely correlated with the four letters of the Tetragrammaton, and Beriah, the second world, is assigned the first He, the letter of expansive, receptive form, read in this scheme as the point where Atziluth's undifferentiated radiance first takes on the beginning of structure, without yet becoming as dense as the worlds below it. The correspondence layers a second structure onto the four worlds, treating the descent from Atziluth to Assiah as, at once, the spelling out of a single divine name.
Kabbalistic teaching holds that Beriah, like each of the Four Worlds, contains a complete Tree of Life within it, its own ten sefirot, so that the world of the Throne and the great Archangels is not simply a rung below Atziluth but a whole structure in miniature, receiving Atziluth's tree above it and passing its own downward into Yetzirah. This repeated, nested pattern is the basis for describing the Four Worlds as a ladder rather than a simple list.
Beriah corresponds in the soul scheme to Neshamah, the higher intellective soul, placing the human faculty of understanding at the same rung as the world of pure creative mind, the level associated in Jewish mourning custom with continued study on a departed relative's behalf.
Sources The ZoharTraditionally attributed to Moses de Leon with Encyclopaedia Judaica, 2nd editionMichael Berenbaum and Fred Skolnik (eds.)