Answer: Unity means that according to all the desires of the Giver and the receiver, the two unite with one another like the guest and the Host in Baal HaSulam’s famous example.
The guest has nothing to give to the Host besides his attitude, provided that he develops the same attitude to the Host as the Host has to him. Meaning, we don’t take into consideration the fact that the guest uses his appetite, and the Host—his power. They are initially this way: one is the Creator, and the other is creation.
But if we remove these initial conditions, the fact that one is the Creator and the other is creation, since they have to attain total equality, then by what criterion can they be equal? According to their attitude, which they build without any connection to what existed before.
That is, we must ascend in the relationships between us so it wouldn’t matter that He is the Creator, He is primary, and He created me in the desire to enjoy and does anything He wants with me because all of this initially comes from Him, being the upper root. And it doesn’t matter that I, the creation, am unable to do anything more than that.
However, if He and I attain this state where we have absolutely equal opportunities, then out of our equal opportunities we desire to attain adhesion and unity. First of all, the Creator and creation have to attain the state where they are both completely equal and independent from one another—the creation from the Creator and the Creator from the creation.
Once we are equal and we have the opportunity to create any connection between us that each of us freely desires, we attain the state where we desire only love, unity, and adhesion between us.
As Baal HaSulam explains, the guest and the Host reach a state where they depend on one another in equal measure: the Host on the guest and the guest on the Host, like children and parents. Then the will to enjoy contained in creation and the will to bestow that the Creator has both harness one another and obligate each other. And even though on one hand the Creator is able to do anything, this does not indicate anything because He feels love for creation and this love limits Him, enabling Him to do only what love dictates, rather than everything He can do.
That means that the force of love is the force of restriction, the reverse force operating in the Creator. It does not let you do anything. You cannot destroy the person you love. Love rules.
Therefore, the condition of unity is equality—in opportunities, forces, abilities, and freedom of expression. Once the equality is there, then out of all of these opportunities we activate precisely the force of love and attain unity.
From the 2nd part of the Daily Kabbalah Lesson 2/14/11, The Zohar