The second principle is the explanation of the ten sefirot and the four worlds of Atzilut (Emanation), Beria (Creation), Yetzira (Formation), and Asiya (Actualization), which are four levels, one below the other, through which the will to receive must devolve until the vessel is established properly as an entity in itself.
The third principle is the constriction (tzimtzum) and the partition that was formed upon this receiving vessel, which is the fourth level. This fourth level was then replaced by new receiving vessels in the form of ten sefirot called the returning light.21The returning light is the supernal light that was rebuffed when it impacted against the partition>>. Since the supernal light is comprised of ten sefirot, so too is the returning light comprised of ten sefirot.