Likutei Moharan 219:2/ליקוטי מוהר"ן רי״ט:ב׳

12. I heard more in [Rebbe Nachman’s] name on this subject, that [God] covered and constricted His majesty in order to reveal His Kingship. [The Rebbe] then mentioned what he had said the previous day. The point is that fear, the aspect of kingship, is the aspect of submissiveness. This is what is written, “What does God your Lord ask of you? Only that you fear [Him]” (Deuteronomy 10:12). The Holy One lessens Himself, as it were, and asks from them fear. For “ask of you” is the aspect of submissiveness and humility, like one who asks and requests from a friend.

2For fear is the aspect of malkhut (kingship), as it is written (Avot 3:2), “Were it not for the fear of the malkhut (government),” {as has been brought a number of times}. And malkhut is the aspect of poverty and submissiveness, for there can be no king unless there are subjects. This is the aspect of poverty—it has nothing of its own (Zohar I, 238a), {as has been brought elsewhere}. That is, the attribute of malkhut has nothing whatsoever of its own. It is only by means of the world that the attribute of malkhut is revealed, for there can be no king unless there are subjects. Thus it is that the attribute of malkhut, which is the aspect of fear, is the aspect of poverty and submissiveness.

3Therefore, at the Giving of the Torah, when the Holy One wanted to reveal His Malkhut and the fear of Him, God submitted Himself to the Jewish people, as it were, and requested of them that they accept His Kingship. He gave them a number of assurances, as it is written (Exodus 19:6), “You will be to Me a kingdom of priests and a holy nation….” All these assurances are the aspect of submissiveness. This was all in order to reveal His Malkhut and the fear of Him, as it is written (Exodus 20:17), “in order that the fear of Him be on your faces.” For all this was for the sake of fear, which is the aspect of malkhut, as explained above. God lessened Himself in order to reveal His Kingship, as explained above.

4This is the explanation of “God is King; He donned majesty.” “God is King”—that is, when the Holy One wanted to reveal his Kingship, then “He donned majesty”—He clothed and contracted His majesty, and lessened Himself, as it were, as explained above.