Source: A letter of the Rebbe, 22 Sivan 5704: Igros Kodesh, vol. 1, no. 156, section 2.
In the Alter Rebbe's Shulchan Aruch: Orach Chaim, Siman 25, seif 23.
1. The Two Opinions on Tefillin Blessings
There are two primary opinions cited in the Shulchan Aruch—the Code of Jewish Law—regarding the blessings recited when donning tefillin. According to the first view, which is our common practice, one recites the blessing l'haniach tefillin—to put on tefillin—when putting on the shel yad (the hand tefillin), and has in mind that this blessing should also cover the shel rosh (the head tefillin). A second blessing, al mitzvas tefillin—on the mitzvah of tefillin—is only recited for the shel rosh if there was an interruption, such as speaking, between putting on the two tefillin.
2. The Alternative Custom: Two Blessings Always
The other opinion maintains that one should always recite a separate blessing on the shel rosh, regardless of whether there was an interruption. In this custom, after making l'haniach tefillin on the shel yad, one also says al mitzvas tefillin upon donning the shel rosh. To address concerns about possibly making an unnecessary blessing, they add the phrase baruch shem kevod malchuso leolam vaed—blessed be the name of His glorious kingdom forever and ever—afterwards. This serves as a safeguard in case halacha follows the first opinion.
3. The Alter Rebbe’s Rulings: Shulchan Aruch vs. Siddur
Within his own works, the Alter Rebbe presents both approaches. In his edition of the Shulchan Aruch, he writes that the custom in these lands follows the second opinion: two blessings should be made, one for each tefillin. However, in his Siddur, which reflects later rulings and often aligns with Kabbalistic practice, he instructs to make only one blessing (l'haniach tefillin) and to have in mind both the hand and head tefillin. Only if there is an interruption does he require a second blessing for the shel rosh. The Siddur’s ruling is considered authoritative for Chabad practice and is based more on Kabbalah than strictly legal considerations.
4. The Zohar’s Position: One or Two Blessings?
A book the Rebbe was commenting on, V'Aseh Tov, claims to have proven that according to the Zohar two blessings should be made—one for each tefillin. The Rebbe answers that this needs clarification, and brings two sources. First, the Tikkunei Zohar Chadash, near its end (Vilna 5627 edition, p. 46b), implies that this is a dispute between the Babylonian Talmud (Bavli) and Jerusalem Talmud (Yerushalmi). According to this reading, the Bavli holds that only one blessing is recited (as explained by Rashi), which matches our custom. It concludes there: "ומסיטרא דעמודא דאמצעיתא - לא צריך אלא ברכתא חדא" ("And from the side of the middle pillar, only one blessing is needed"). See also the Biur HaGra on Orach Chaim 25.
5. Kabbalistic Sources: Pri Etz Chaim and Chassidic Interpretation
The Rebbe further points out that both opinions are brought and explained according to Kabbalah in Shaar HaKavanos, Derushei Tefillas HaShachar, Derush 2 and 3, and that this is mentioned in the maamar Vayomer Hashem Eilav Mi Sam Peh in Torah Or. However, in Pri Etz Chaim, Shaar HaTefillin, ch. 10, a foundational Kabbalistic work, it is stated explicitly: "ולא יברך על ש"ר אם לא שפסק בדיבור" ("And he shall not bless on the shel rosh unless he interrupted by speaking"). This clear statement supports our custom of making only one blessing unless necessary due to an interruption.
6. Reconciling Zohar with Halachic Practice
Given these sources, especially from Pri Etz Chaim, the Rebbe writes that it is difficult to say he would have written this if the view of the Zohar were the opposite: "וקשה לומר שהי' כ' כן אם הי' דעת הזהר להיפך". The Rebbe refers further to Mishnas Chassidim, Maseches Hanachas Tefillin 3:4, and to Shaar HaKollel by R. Avraham David Lavut (2:6). Ultimately, our practice aligns with both halacha and Kabbalah: make one blessing on the shel yad, have in mind both tefillin, and only recite a second blessing if there was an interruption before putting on the shel rosh.