Da’at is Zeir Anpin that unites Chochmah and Binah that are Aba and Ima These father, mother and son are called Chochmah, Binah and Da’at; for when the son, Zeir Anpin, takes the signs of his father and mother – that is, when he receives and incorporates Chochmah and Binah of Aba and Ima into himself - he is called Da’at, which is derived from edut (testimony), which is the testimony of both, as he includes within himself the brains of Aba and of Ima; Da’at reconciles and incorporates Chochmah and Binah.
This son, who is Da’at, is called a firstborn son, as written, “Israel is my son, my firstborn” (Shemot 4:22). Zeir Anpin, who is Da’at, is called Israel; it is said of him, “Israel is my son, my firstborn.” And since he is called the firstborn, he receives two portions – a portion from Aba, who is Chochmah, and a portion from Ima, who is Binah. When he grows with his crowns, he receives three portions; they are Chochmah, Binah and Da’at, based on the meaning of, “three coming out of one, one is present in three.”
In any case, two portions and three portions are the same; Da’at has no more than the inclusion of Chochmah and Binah in such a way that even Chochmah, Binah and Da’at are no more than two – Chochmah and Binah. Both are the same, since Da’at receives the inheritance of his father and mother and so has but Chochmah and Binah like his father and mother, no more.