Understand what is explained in Shulchan Aruch (Set Table — the Jewish code of Law): the rule is that one should repeatedly reflect upon the prayers of the Terrible Days so that when prayer time comes, he will be accustomed and used to praying.
The thing is that the prayer should be in the heart. This is the meaning of the work in the heart, that the heart will agree to what one says with one’s mouth (otherwise, it is deceit, that is, one’s mouth and heart are not the same). Hence, on the month of Elul one should accustom oneself to the great work.
And the most important thing is that one can say “write us to life.” This means that when one says “write us to life,” the heart, too, should agree (so it will not be as flattery) that one’s mouth and heart will be the same, “for man looketh on the outward appearance, but the Lord looketh on the heart.”
Accordingly, when one cries, “write us to life,” “life” means adhesion with the Life of Lives, which is by that specifically, when one wants to work entirely in the form of bestowal, and that all of one’s thoughts for self-gratification will be revoked. Then, when one feels what he is saying, his heart can fear lest his prayer will be accepted, that is, that he will have no desire whatsoever for himself.
And concerning self-gratification, there appears a state where it seems that one leaves all the pleasures of this world, all the people, friends, his kin, all his possessions, and retires to the desert where there is nothing but wild beasts, without anyone knowing of him and of his existence. It seems to him as though he loses his world all at once, and feels that he is losing a world filled with liveliness, and takes upon himself death from this world. He feels as though he is committing suicide, when he experiences this image.
Sometimes, the Sitra Achra helps him picture his state with all the dark colors. Then the body repels this prayer, and in such a state, one’s prayer cannot be accepted, since he himself does not want his prayer to be accepted.
For this reason there must be preparation for the prayer, to accustom oneself to the prayer, as though his mouth and heart are equal. And the heart can come to agree through accustoming, so it would understand that reception means separation, and that the most important is the adhesion with the Life of Lives, which is bestowal.
One must always delve in the work of Malchut, called “writing,” considered “ink” and Shacharit (blackness). This means that one should want one’s work to be in the form of “Libni and Shimei,” [1] that only at the time of whiteness does he adhere to the Torah and Mitzvot, but unconditionally. Whether in white or in black, it will always be the same for him, and that come-what-may, he will always adhere to the commandments of the Torah and Mitzvot.