The Zohar, Chapter “Chayei Sarah (The Life of Sarah),” Item 155: …But the lower ones cannot receive the illumination of the left before it is clothed in Hassadim from the right line.
Esau wanted to receive the Light of Hochma into the egoistic desires (Kelim of reception) and found that he was unable to do this. Similarly, we spend our whole lives chasing after pleasures, trying to find enjoyment in life, but as soon as we feel pleasure, it immediately disappears. This cycle recurs throughout our entire lives. Repeating this unending cycle is why Esau was weary and said, “I am unable to continue like this. It is hopeless; I am tired of it. I am ready to unite with Jacob.”
Today all of humanity is standing at the threshold of this same realization. For this reason, the science of Kabbalah, Jacob’s method, is being revealed. This science is precisely about how to build the middle line, how to implement Jacob’s method.
Before humanity reached this state of despair, there was no demand for the science of Kabbalah. Now the need is apparent; from here the Torah can be revealed since the Torah is revealed from the middle line – the correction of egoism.