Derekh Hashem, Part Four, On the Daily Order of Prayer

Regarding the control of the forces of impurity at night: The Supreme Wisdom set up that at night, the forces of impurity be given the authority to spread through all of its channels, and for its branches to wander throughout the world. And He intended that at that time, people would gather into their houses, lay down in their beds, sleep and rest until the morning. For [in the morning] the spreading and authority of these forces and all of their branches would be taken away; and people would once again leave to 'their work, until the evening.' And this is what King David, peace be upon him, explained (Psalms 104:20-23), "You bring on darkness and it is night, etc. When the sun shines, etc. Man goes out to his work, etc." However all of these matters - in all of their demarcations and measures - are rooted in the roots of the foundations of [God's] direction, according to all of its influences that come to the creatures at all of their levels, as it is written in Part I (On the Spiritual Realm 3), see there. But you should know that even though it is said by way of generalization, that the night is the time that these forces are given authority, note that it is actually only given during the first half of the night. But from midnight, an influence of emanation and will flows from in front of Him, may He be blessed, to all of the worlds. And authority is [then] taken from the forces of evil; and their branches are driven away from the place of civilization. So the emanation of the day begins to be aroused until the day is brightened by [the sun's rise]. And then the proper influence is brought down and all of existence is renewed. However the matter of this authority of these forces at night and their being driven away is a thing that is embedded into the nature of the world and its arrangements. [It is] beyond the authority and submission that comes to them from the actions of man. And that is that the Supreme Wisdom determined that since the existence of true good and evil is something that follows from the actions of the ones with free choice, it was necessary that there be an avenue within the natural axioms of the world for evil to have authority in it in such a way that it would be possible for this evil to spread in parts of it, as well as its being prevented from spreading [in other parts of it]. And truly since this is so, the Supreme Wisdom decreed that it be appropriate that there be one part in time itself, in which He would give it authority and [the possibility] to spread on its own. And see that it is the schema upon which it is possible to add from the actions of man. And [It likewise decreed] that there be another part in which authority would be taken away from it, such that there be a basis in which it be possible for [man's] actions to be the [sole] cause. And behold that the two powerful entities of light and darkness follow from the angle of [God's] emanation and its absence, as we explained in Part I (On the Purpose of Creation 3); and He gave them [each] a portion in time, meaning day and night. And the authority of the powers of impurity - that we mentioned - and their being driven out follow [these times]. But it is all [only] the substructure for the effects of the actions [of man], as we have mentioned.