Answer: It means to do everything in your power to unite with others, and in that bond to reveal the common bestowing force, the Creator. But you do it precisely because you fulfill His desire to be revealed to the creatures. To this end they must prepare an altruistic desire in which the Creator’s force of bestowal will be revealed. The creatures will reveal a need for love, and the Creator will be revealed as Love.
In order to connect to others, I need a screen. Otherwise I cannot unite with anyone, as I desire only to consume everything within. Therefore, don’t think that you are capable of unifying on your own: It’s the upper Light that unites us. It puts a screen before me over my own ego and raises me over it, where it concerns my heart, the concentration of desire. And it is there, in the space above it, where the source of all my desires, goals, and aspirations is transferred. Like a mother who as if exits herself and lives within her child.
This kind of attitude is called Yesher (straight line), but before this my desire was Igulim (circular). To the degree that I can make a straight intention toward others, it means that I have built a “straight line.”
Now I exist in a straight desire, but it is similar to the Surrounding Light, or circles. This is somewhat of a paradox. In my ego I am similar to the Light; the Light is circular in its bestowal and I am a circular egoist, open to everybody.
But in my work, I am like a straight line, which is opposite to the Light, for the Light is circular. How do we then connect together? The circles and the straight line are connected by the restriction done within them both. It is thanks to this restriction that a mutual point arises—their point of contact.
From the 3rd part of the Daily Kabbalah Lesson 6/7/12, The Study of the Ten Sefirot