"G‑d remembered Sarah as He had said, and G‑d did what he had promised for Sarah. And Sarah conceived and bore Abraham a son in his old age, at the set time of which G‑d had spoken to him." (Gen. 21:1-2)
"Whoever prays for mercy on behalf of his friend, and he needs the same thing, will be answered first." (Baba Kama 92a)
It is known what the Sages said on the verse "Ruler over men shall be the tzadik; he that rules with the fear of G‑d." (Samuel II 23:2): "Who rules over Me? The tzadik; for the Holy One decrees and the tzadik annuls." (Moed Katan 16b)
The full verse from Samuel reads: "The G‑d of Israel said, The Rock of Israel spoke to me; 'Ruler over men shall be the righteous; he that rules with the fear of G‑d." However, by changing the punctuation, the Sages derive a different reading of this verse: "The Rock of Israel is ruler over men; the righteous rules over G‑d."
How does he annul G‑d's decree? The answer is as follows:
Judgments are only sweetened in their root....
All evil and suffering are judgments, and judgments are only sweetened in their root, as the Zohar says, "From the side of bina, the judgments issue forth." (Zohar II:175b, See also Zohar III:65a) The tzadik raises all the judgments to bina, where they are sweetened in their root.
According to this, we can understand why a tzadik is unable to do this for himself. That is, when he himself suffers, he is unable to raise the judgments to bina. And although our Rabbis have stated, "A prisoner cannot release himself from jail," (Berachot 5b) we still need to understand why.
The reason is that he can only achieve this through daat (lit. knowledge), and what can he do when they take the daat and the mochin away from him? Therefore, he can't help himself at all. For this reason, it is a great mitzvah for others to pray for him and uplift the judgments.
When the judgments are raised to the Gate of Nothingness, they are rectified....
In Chasidism, "daat" refers to a state of mystical attachment to G‑d. "Mochin" (literally "minds") refers to a state of expanded consciousness - "mochin d'gadlut" - which accompanies daat. When a tzadik is in such a state, he can annul all states of narrowness and constriction - whether physical or mental. There are the roots of suffering. He annuls the judgments by lifting them to their root. There, they are annulled in the light of the Infinite. However, when he himself has fallen into a state of constricted consciousness, he is unable to free himself.
Now, to understand how the judgments are sweetened in their root, and the meaning of the statement "From the side of bina, the judgments issue forth", we must know that there are fifty gates of bina. Forty-nine gates are called "her side" [i.e. the side of bina]. From there, the judgments issue forth. However, the fiftieth gate is called "ayin" ["nothingness", a reference to the sefira of keter, which reveals the infinite "Nothingness" of the G‑d-head, beyond all limitation and perception], where there is complete mercy, with no judgments at all. Therefore, when the judgments are raised to the Gate of Nothingness, they are rectified....
Therefore, the Baal Shem Tov explained the statement of the Rabbis "One who prays on his friend's behalf is answered first." Why is he answered first? Because he must uplift the gevurot and the judgments to their roots, and he is there [i.e. in the Fiftieth Gate] first. Afterward, he draws down [illumination] upon the stricken person as well. Thus, he is answered first.
[Adapted by Eliezer Shore from Sefer Baal Shem Tov, Vayera.
Reprinted with permission from www.baalshemtov.org]