וכמו שכתוב: וישוב אל הוי׳ וירחמהו

As the verse states:6 “He shall return to G‑d and He will have compassion for him”; i.e., the sinner shall return to G‑d and have compassion for Him.

But how are we to understand the concept of arousing mercy for the Tetragrammaton?

פירוש: לעורר רחמים על השפעת שם הוי׳ ברוך הוא, שנשתלשלה וירדה תוך היכלות הסטרא אחרא הטמאים להחיותם

This means, arousing compassion for the life-giving power issuing from the Four-Letter Name, that has descended by stages into the chambers of the impure sitra achra, to give them vitality.

על ידי מעשה אנוש ותחבולותיו ומחשבותיו הרעים

[This descent was brought about] by the deeds of man, and his evil schemes and thoughts.

Evil thoughts alone suffice to make the vitality descend into the chambers of the kelipot and sitra achra.

וכמו שכתוב: מלך אסור ברהטים, ברהיטי מוחא וכו׳

As the verse says,7 “The king is bound with gutters,” [which is interpreted to mean that “the King is bound] with the gutters of the mind….”8

As explained by the Rebbe, the image is of the various channels and gutters of the mind through which thoughts, like gushing currents, rush fleetingly. Thus, even transient evil thoughts that one harbors ephemerally can bind and shackle the King; they can exile the flow of vitality emanating from the Four-Letter Name of G‑d.

היא בחינת גלות השכינה כנ״ל

And this state, as noted above,9 is the exile of the Shechinah — the Divine Presence, the level of Malchut (“Kingship”) of the World of Atzilut.

וזמן המסוגל לזה הוא בתיקון חצות

The auspicious time for this [arousal of compassion] is Tikkun Chatzot, the midnight lament for the exile of the Divine Presence,

כמו שכתוב בסדור בהערה, עיין שם באריכות

as pointed out in the note to Tikkun Chatzot in the Siddur; see there at length.

וזה שכתוב שם: נפלה עטרת ראשינו, אוי נא לנו כי חטאנו

We thus find [in that prayer], “The crown of our head is fallen; woe to us, for we have sinned”; i.e., sin causes the soul’s Source (“the crown of our head”) to topple into the depths of the kelipot and sitra achra.

ולכן נקרא הקב״ה מלך עלוב בפרקי היכלות, כמו שכתב הרמ״ק ז״ל

Therefore the Holy One, blessed be He, is called the “humiliated King” in Pirkei Heichalot,10 as R. Moshe Cordovero wrote,

כי אין לך עלבון גדול מזה

for there is no humiliation deeper than this, than the ignominy of exile within the realm of the kelipot.

ובפרט כאשר יתבונן המשכיל בגדולת אין סוף ברוך הוא, ממלא כל עלמין וסובב כל עלמין

Especially when a thoughtful person meditates on the greatness of the Infinite One, Who permeates all worlds and encompasses all worlds, for G‑d provides vitality to created beings both in a manner which “permeates” each recipient according to its individual capacity, as well as in a manner that transcends and “encompasses” them,

כל אחד ואחד לפי שיעור שכלו והבנתו

each person [meditating upon G‑d’s greatness] according to the range of his intellect and understanding,

יתמרמר על זה מאד מאד

he will be extremely grieved over this.

The richer one’s perception of G‑d’s majesty, the more intense will be his feeling of compassion for his own soul and for its Source, the bound and humiliated King.