Baal HaSulam, The Study of the Ten Sefirot, Part 1, “Table of Questions and Answers for the Meaning of the Words“: Question 39: What is the Middle Point (Nekuda Emtzait)? This is the name of Behina Dalet (phase four) in Ein Sof (Infinity). She is named after her unification with Ohr Ein Sof (the Light of Infinity).
We begin to perceive ourselves, our existence, only after having reached the fourth phase. This is because we can only feel our own being in contrast to its opposite: the upper root.
This feeling is revealed at the last, fourth phase of the fourth phase (Behina Dalet de Dalet). This is because the fourth phase is the desire to enjoy starting to get to know herself. All of the previous phases have to be revealed inside of her.
Phases zero, one, two, and three are separated from the root and build themselves inside of the fourth phase. The last, fourth phase gathers up the experience of all of these phases and reveals herself and her relationship toward Him, that is, attains what the upper one is doing with her, relative to them.
This fourth phase of the fourth phase discovers herself as the desire to enjoy. In her upper part, she comes to the understanding and attainment of the root, while at the bottom part, her own relationship, the reaction to the revelation of the Creator’s relationship to her, is already apparent. This reaction is the feeling of shame that makes her perform the First Restriction (Tzimtzum Aleph).
As it is written, this phase is called the middle point (Nekuda Emtzait) “after her unification with Ohr Ein Sof (the Light of Infinity),” meaning that all of the Light of infinity is revealed in her before she feels the shame and decides to perform the restriction.
All of this is concentrated inside the fourth phase (Dalet) at the borderline where her upper part ends. In this part she senses the Creator’s attitude toward her and thus cleaves to Him, meaning that she is included into Him and annuls herself before this Light, the Creator’s love.
This happens exactly at the border, after which the lower part and a new revelation begin. In the state of her merging with the Creator, where she attains her full unity with the Light and loyalty to Him with all of her heart and soul by virtue of her nature, at the very depth of this unity, she suddenly discovers a quality in the Creator to which she cannot connect.
This is because now sbe is not connected to the Creator Himself, but to the fulfillment that she is receiving from Him. That is why she feels their connection as an imperfect one. There is one more quality in the Creator, the quality of the giving one, and she is not able to connect to this quality. That is why she begins to feel shame. In the very depth of her connection to and dependence on Him, like that of a baby feeding completely from the mother, she discovers that He is opposite to her.
This arouses terrible shame inside of her because she is located right inside the Creator, in the closest connection to Him. This feeling of shame builds the four reverse phases when she decides what to do with this discrepancy and comes from the root of feeling the shame to its fourth phase, to the decision to restrict herself and not receive the Light anymore. Now, she begins to search for how to merge under the conditions of equality and similarity of qualities, and not by restricting herself and becoming one who is fully receiving.
This is the middle point, the one that was completely merged with the Creator before it started to burn with shame and all subsequent actions took place.
From the 3rd part of the Daily Kabbalah Lesson 6/27/2011, Talmud Eser Sefirot