Here we have the concept of the “center” of Eyn Sof mentioned in Kabbalistic literature (Etz Chayim, Derushey Igulim VeYosher 11:3), where the Tzimtzum (“contraction”) took place. This “center” is the central “point” on the basis of which the worlds and the service within them were created. The act by which they came about was the concealment of perfection, which left a realm governed by the principle of imperfection, a realm in which service is relevant.
However, what He wanted to reveal is how the realm of deficiencies becomes rectified through the power of His oneness. If so, the work is not complete unless perfection is initially concealed, to make it possible for deficiencies to exist. In this phase, the possibility of service exists – until the perfection of His oneness and unity is revealed and He rectifies all the deficiencies.