וזהו שאומרים: אשר קדשנו במצותיו

This is the meaning of the text of the various blessings pronounced before one fulfills a mitzvah: “[Blessed be He] Who has betrothed us by His commandments”:

The Hebrew word kidshanu — generally rendered, “Who has sanctified us” — is here rendered, “Who has betrothed us,” from the Hebrew word kiddushin (“betrothal”). For mitzvot too, are:

כאדם המקדש אשה, להיות מיוחדת עמו ביחוד גמור, כמו שכתוב: ודבק באשתו והיו לבשר אחד

like a man who betrothes a wife, so that she be united with him in a perfect bond, as it is written:11 “And he shall cleave to his wife, and they shall be one flesh.”

ככה ממש, ויתר על כן לאין קץ, הוא יחוד נפש האלקית העוסקת בתורה ומצות, ונפש החיונית ולבושיהן הנ״ל, באור אין סוף ברוך הוא

Exactly similar to the unity achieved through betrothal, and even infinitely surpassing it, is the union of the divine soul that is engaged in Torah and the commandments, and of the vivifying soul, and their garments referred to above, viz., thought, speech and action — all of them becoming united with the light of the blessed Ein Sof.

This spiritual union infinitely surpasses the physical union of man and wife. The correlation to a physical union is valid only in the sense that in this world there can be no greater union than that of man and wife. This union is termed kiddushin.

ולכן המשיל שלמה עליו השלום בשיר השירים יחוד זה ליחוד חתן וכלה

Therefore did Solomon, peace unto him, in the Song of Songs compare this union of G‑d and Jews through Torah and mitzvot with the union of bridegroom and bride,

בדביקה חשיקה וחפיצה, בחיבוק ונישוק

this union being with attachment — an external level of unity, with longing — a more inward level of unity, and desire — an even more inward level of unity, with embrace and kissing.

All the above manners of union are found in the Jew’s relationship to G‑d through Torah and mitzvot.

Until now the Alter Rebbe expounded on the theme of unity, understanding kidshanu as deriving from kiddushin (“betrothal”). The Alter Rebbe now goes on to say that the word kidshanu also alludes to the sanctification a Jew achieves through Torah and mitzvot, sanctification implying a state of exaltation and separation from all worlds.

וזהו שאומרים: אשר קדשנו במצותיו

This is also the meaning of the blessings alluded to above: “Who has sanctified us by His commandments,” the verb kidshanu (“Who has sanctified us”) here meaning:

שהעלנו למעלת קודש העליון, ברוך הוא, שהיא קדושתו של הקב״ה בכבודו ובעצמו

that He has elevated us to the heights of the Supreme Holiness, which is the holiness of the Holy One, blessed be He, Himself.

וקדושה היא לשון הבדלה, מה שהקב״ה הוא מובדל מהעולמות

Kedushah (“holiness”) is a term indicating separateness, in that the Holy One, blessed be He, is apart from the worlds,

והיא בחינת סובב כל עלמין, מה שאינו יכול להתלבש בהן

this being the quality of “encompassing all worlds,” being unable to clothe Himself within them.

Because of the inability of created beings to absorb the extreme holiness of this transcendent level, G‑d (as it were) cannot enclothe Himself within the worlds, and therefore affects them in an encompassing manner. It is to this lofty level that Jews are elevated through their performance of mitzvot.

כי על ידי יחוד הנפש והתכללותה באור אין סוף ברוך הוא, הרי היא במעלת ומדרגת קדושת אין סוף ברוך הוא ממש

For through the union of the soul with, and its absorption into, the light of the Ein Sof, it attains the quality and the degree of holiness of the blessed Ein Sof Himself,

מאחר שמתייחדת ומתכללת בו יתברך, והיו לאחדים ממש

since it unites itself with Him, and is integrated into Him, and they become truly one.

וזהו שכתוב: והייתם לי קדושים כי קדוש אני ה׳, ואבדיל אתכם מן העמים להיות לי

This is the meaning of the verse:12 “And you shall be holy unto Me, for I the Lord am holy; the verse gives us the reason for the Jew’s sanctity, connecting it with G‑d’s Supreme Holiness, which Jews can attain through Torah and mitzvot; and I have separated you from other peoples that you should be Mine.” Here we see that holiness implies separation, as mentioned earlier.

ואומר: ועשיתם את כל מצותי והייתם קדושים לאלקיכם, אני ה׳ אלקיכם וגו׳

Another verse states:13 “You shall fulfill all My commandments and be holy unto your G‑d: I am the Lord your G‑d….” The term “your G‑d,” in the possessive form, recalls the relationship set up when a man betrothes a woman, whereby she becomes his wife.14

-פירוש: כי על ידי קיום המצות הריני אלוה שלכם

The meaning is that “through the fulfillment of the commandments I become ‘your’ G‑d,” in the same manner

כמו אלקי אברהם, אלקי יצחק וכו׳

as G‑d is called “the G‑d of Abraham,” “the G‑d of Isaac,” and so on,

שנקרא כן מפני שהאבות היו בחינת מרכבה לו יתברך

called thus because the Patriarchs were on the level of a “vehicle” unto Him,

The Patriarchs were totally dedicated to G‑d, and nullified before Him, like a vehicle (lit., “chariot”) which is totally nullified to its driver, possessing no independent will.

ובטלים ונכללים באורו

and they were nullified and absorbed in His light.

וככה הוא בכל נפש מישראל, בשעת עסק התורה והמצות

So it is with the soul of every Jew at the time he is occupied with Torah and the commandments.

When a Jew occupies himself with Torah study and the performance of its commandments he is totally nullified and absorbed in G‑d’s light. The only difference between the Patriarchs and other Jews is that the Patriarchs were in this state constantly, while other Jews attain this level only at the above-mentioned times.