“Introduction to The Book of Zohar,” “The Donkey Driver,” Item 87: The donkey driver is the impregnation of the soul of a righteous that comes to assist those who walk on the path of the Creator, to exit his degree and arrive at a more important degree, like those donkey drivers who take people from place to place on their donkeys. At that time, the righteous, too, falls from his previous degree and comes to an impregnation of a new degree, like the soul that comes to assist him. Impregnation means departure of the Mochin.
You should know that this applies to any new degree, since as long as one needs to receive a new degree, he must arrive at the departure of the previous Mochin. And as he previously never had any degree to begin the acquiring of the soul anew, which is called Ibur, then Yenika, which is the Light of Ruach, she therefore said that because of that, “My son, go and drive the donkeys.” Because it is impossible to extend anything from the previous degree, you must start the Ibur anew, and this is called “donkey driving.”
We shouldn’t be scared that we start the work anew each time from the same place that we were seemingly before and repeat it over and over again. If a person is given a state of descent, it’s actually a sign of advancement! This means that he isn’t simply thrown into the corporeal life but is also given the feeling that he has descended. This means that he has completed the previous level and is now starting a new level that he lacks for the completion of his vessel.
From the 4th part of the Daily Kabbalah Lesson 2/16/14, Writings of Baal HaSulam