The secret of Purim, as is known, is that during the entire period of the Exile, Nukva / Rachel stands back-to-back with Zeir Anpin.

This is a kind of union, greatly inferior to that of face-to-face, which characterizes the Redemption, as well as other states of influx of divine mercy. The concept of "back-to-back" can be understood as a type of defense mechanism meant to ensure that Nukva / Rachel's vulnerable back side is not in danger of "attack" by the External Forces, which are usually prevalent in her realm.

[The story of Purim] occurred at the end of the [divinely decreed] 70 years of the Babylonian Exile, as is known. At that point in time, the rectification process began in the supernal regions, whereby they would be returned [in a union of] face-to-face. [In order for this to come about,] it was necessary that Zeir Anpin be rendered unconscious, meaning that Zeir Anpin's mochin leave [him] and enter Rachel, thus rectifying her partzuf. [As a result,] she is then able to return [to Zeir Anpin] face-to-face.

The end of Zeir Anpin's being rendered unconscious occurred in the days of Mordechai….

Like Siamese twins joined at the back, the operation to separate Zeir Anpin and Nukva first entails the "anaesthetization", i.e. the departure of consciousness, of Zeir Anpin. Nukva then receives this consciousness indirectly, via Imma, which "enlightens" her, causing the External Forces to flee. The above union of "face-to-face" can only occur when the External Forces below are nullified to the extent when they cannot feed off, i.e. endanger, her.

The end of [this general process] of Zeir Anpin's being rendered unconscious occurred in the days of Mordechai. This is the secret of Haman's declaration: There exists [in Hebrew, "yeshno"]a nation scattered about and dispersed (Esther 3:8), about which the Sages commented that Haman's declaration, "There exists" [in Hebrew, "yeshno"], meant "Their god is sleeping [in Hebrew, 'yoshen', a play on words with 'yeshno', above] (Midrash Rabba Esther, 7:12 and Pirkei D'Rabbi Eliezer, section 50); when he said "…is sleeping", he was referring to their king - Zeir Anpin.

Like a king, which influences and provides for his nation, Zeir Anpin (usually) provides sustenance to Nukva.

[Translated and edited from Pri Etz Chaim.]