“Neither shall you lack the salt of the covenant of your God from your offering.” Why is salt so important? It is because it cleanses and perfumes the bitter, and makes it tasty. Salt is Dinim [judgments] in the Masach [screen] of Hirik, on which the middle line emerges, which unites the right with the left. It cleanses, perfumes, and sweetens the Dinim of the left, which are bitter, with the Hassadim [mercies] on the right line. Had there not been salt, the middle line would not have been extended and the world would not have been able to tolerate the bitterness.
Zohar or All, VaYechi [Jacob Lived], Item 666
Salt is the basis of all the spices, adding flavor to the food. In spirituality, when we begin to receive the upper light into the soul, it is regarded as flavors spreading within us.
Our evil inclination, the egoistic material of which we are made, is like a stew without spices. We derive no pleasure from it. This is why it was said (Babylonian Talmud, Kidushin, 30b), “I have created the evil inclination; I have created for it the Torah as a spice.” With the additional spice that the upper light brings—using the right intention—that same substance acquires wondrous flavors. Then, we have an evil inclination, and next to it, The Zohar as a spice. The combination between them yields the middle line.
If there weren’t salt, the middle line would not have been drawn and the world would not be able to tolerate the bitterness, says The Zohar. In other words, if we could not mitigate the ego, we would not be able to tolerate it.