ומקדושה זו נמשכת קדושה עליונה על האדם למטה לסייעו סיוע רב ועצום לעבודתו יתברך

From this holiness, a sublime holiness issues forth upon man below, to assist him with a great and powerful aid in his service of G‑d.

וזהו שאמרו רז״ל: אדם מקדש עצמו מעט למטה, מקדשין אותו הרבה מלמעלה

This is what our Sages meant when they said: 1 “If a man consecrates himself in a small measure here below, he is sanctified greatly from above.”

לבד מה שמקיים מצות עשה של תורה: והתקדשתם וכו׳, כשמקדש עצמו במותר לו

This is apart from the fact that when one sanctifies himself in permissible matters, he thereby fulfills the positive commandment of the Torah: 2 “Sanctify yourselves, and be holy.”

Hence, apart from the consolation previously offered the Beinoni — that through “turning away from evil” by combating evil thoughts and desires, he affords G‑d a pleasure that tzaddikim cannot — his battle with the sitra achra also contains a positive quality in the category of “doing good,” that is likewise not present in the divine service of tzaddikim. 3 This positive quality is the fulfillment of the mitzvah: “Sanctify yourselves…,” which applies only to Beinonim, not to tzaddikim. For the intention of the commandment is that even one’s personal, permissible, and mundane matters should not be attended to out of the desire of one’s animal soul, but for the sake of G‑d. This directive cannot apply to tzaddikim, who are unencumbered by desires of the animal soul, as the Alter Rebbe continues:

ופירוש והתקדשתם: שתעשו עצמכם קדושים

The meaning of “Sanctify yourselves” is: “You shall make yourselves holy.”

כלומר: אף שבאמת אינו קדוש ומובדל מסטרא אחרא

That is to say, although in truth one is not holy and separated from the sitra achra,

כי היא בתקפה ובגבורתה כתולדתה בחלל השמאלי

for the sitra achra of his animal soul is still, as at birth, at its full strength and might, in the left part of his heart — the seat of the animal soul and evil inclination,

The word kedushah (“holiness”) means “setting apart,” i.e., separation from the unholy. 4 The verse thus means: One should sanctify himself even if he must yet make himself holy and separate from the sitra achra, for at his present level his heart still desires those things that derive from it,

רק שכובש יצרו ומקדש עצמו

yet if even while at this level he subdues and masters his evil impulse and makes himself “holy”, separate from the sitra achra, then, continues the verse:

והייתם קדושים

“You will be holy.”

The words “be holy” which, in their simple sense, voice a command, can also be understood as conveying a promise,

כלומר: סופו להיות קדוש ומובדל באמת מהסטרא אחרא

meaning that ultimately he will be truly “holy” and removed from the sitra achra,

על ידי שמקדשים אותו הרבה מלמעלה

through his being “greatly sanctified from above,” as quoted earlier from the Gemara,

ומסייעים אותו לגרשה מלבו, מעט מעט

and through his being aided from above to expel [the sitra achra] from his heart, little by little, so that even in his heart he will no longer have any desire for anything originating in the realm of the sitra achra.