Since the unlimited is conceived as being beyond all things, and the sacred cannot be limited in any way, the very existence of the world is an insoluble riddle.
And it does not matter whether the world is real or imaginary; even an imagined world cannot be resolved by saying that the Ein Sof (*) is beyond all limits.
From this point of view, the Divine, the more high and mighty He is, obligates Himself, in a certain sense, also to be closer than anything else to the reality of the world we recognize.
Hence, the existence of matter, which is the other extreme of Divine hiddenness, is possible only by virtue of the power of the unlimited, which gives everything its existence.
The existence of the world, by being dependent on the unlimited, requires that the unlimited should be confined to some limit.
In other terms, since one cannot say that the Ein Sof is confined in any way, one has to presume that the Ein Sof, which is beyond all possible grasp, is the only basis for all these things that are graspable.
The creation of a limit, or what is called the attribute of Malchut, the attribute of Divine concentration and withdrawal, is related in a very special way to the Infinite Ein Sof.
–Rabbi Adin Steinsaltz
From The Sustaining Utterance by Rabbi Adin Steinsaltz
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(*) Ein Sof ("the Infinite [One]") A term in Kabbalah that refers to God as He exists above and beyond every limitation and definition.
Although the term is only a negative characterization of God, it constitutes a kind of definition, and hence it cannot be accepted as characterization of God's essential being, which is above all definition, even by negation.
Instead, we understand the term as a characterization of the first emanation from God's essential being, an emanation that is sometimes referred to as His Name (see Likkutei Torah, Devarim 7b).
Because the relation between this first emanation and God's essence is comparable to the relation between the light of the sun and the body of the sun, this first emanation is often referred to as Ohr Ein Sof ("the Infinite Light").
–Rabbi Adin Steinsaltz
From the glossary of Learning from the Tanya by Rabbi Adin Steinsaltz