“Just as we cannot grasp the concept of Creation—it is no more than a matter of words for most of us—so we are baffled by the idea of Tzimtzum (God’s hiddenness and withdrawal).
To be sure, we can speak of it and say that it is an explanation of existence.
But all we are saying is that which is infinite can conceal the infinite, which is necessarily all pervasive.
And the problem is not merely a theoretical one; it spills over into the problems of good and evil, light and dark…Because just as God is to be found in Creation, in that which is good, He is also to be found in the opposite of existence, in the negation of life, as well.
As in the saying by the sages: May the good bless thee, oh Lord; but why should not the evil also bless thee!
To be sure, we may claim that it is impossible for the evil to bless God.
On the other hand, we cannot offer up to God only the good, even if we do wish to relate the good and the light to Him and to disclaim the rest.”
From “Concealment as Part of Creation,” p. 57, in The Sustaining Utterance by Rabbi Adin Steinsaltz