When the Shechinah is in exile, the Divine Presence is diminished in the world. The darkness of this world literally eclipses men's minds, and they are incapable of perceiving the Hidden Hand that guides their lives and all history. At such time, the Shechinah is said to return to a prenatal state consisting of ten points all rolled into one, i.e. without any means of expression. This is the exile of the Shechinah as she descends, under the cover of night, into the darkness of evil to search for her children. [Certainly, on a higher level, the Kabbalists warn us that the light of the Shechinah is never actually in exile, never actually diminished. As we say in the Alenu prayer, "The Shechinah of Your Power is in the loftiest heights." From down here in this world, however, and from within the drama of creation, we experience ourselves and the Shechinah in exile; see Zohar 2:216b.]
The Ari goes on to explain that this was actually the state of the Shechinah when G-d first created the world [i.e. when He made the first tzimtzum to create the world as a stage of free will for man, and He was forced, so to speak, to conceal His light and His presence]. It is the state of the Shechinah in exile. On a smaller scale, it is also the state of the Shechinah each night. Each night, that is, creation returns to its primeval state in which God's presence is hidden, the Primal Light becomes totally fragmented [the vessels are broken], and the world becomes a challal [hollow void] wherein G-d's presence is totally undetectable. As noted, the original reason for this was in order to create an environment in which Adam [Mankind] could participate in the perfection of creation. Adam's role was to become the channel through which pure G-d-consciousness could flow into the world. In order to bring this situation about, G-d hid the Original Light [Or Ganuz]. This sweet, awesome, Concealed Light would then only be revealed into the darkness of this world through Adam's conscious efforts. Having participated in its revelation, He would have a portion in its sweetness.