This letter like the previous one was printed in Kovetz Lubavitch, Vol. 11.

[Question:] Please explain the statement in Tanya, Shaar HaYichud VehaEmunah, ch. 7, [that the word] ועד is equivalent to אחד when the letters are exchanged.

Response: This statement has its source in the Zohar, Vol. II, p. 134b. In the commentary, Mikdash Melech — as cited in the marginal notes on the Zohar by Nitzutzei Oros — writes: The alef is exchanged with the vav according to [the scheme of] letters אהו"י and the ches is exchanged with the ayin according to [the scheme of] letters אחה"ע.

The letters אהו"י are related to one another for they are all osios hemshech (i.e., they are drawn after — because of the accent — the letters that appear before them), osios hanoach (i.e., sometimes they are silent and are not pronounced), and osios haneshimah (it is only through them that all the letters are expressed in speech). All of these concepts are stated in the texts of grammar.Seealso the commentary of R. Avraham Ibn Ezra to Shmos 3:15, his riddle (which is included in the introduction to his commentary to the Torah), and the conclusion of sec. 1 in the maamar entitled Es Shabsosai in Likkutei Torah.

Similarly, the letters אחה"ע are all related to each other, because they are all produced by the throat.1

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The above represents the general meaning of the exchange. The explanation why these letters are indeed interchanged with the others can be understood on the basis of the preceding statement in Tanya (quoted from the Zohar, Vol. I, p. 18b) that Shema Yisrael... represents “the sublime unity,” and Baruch Shem..., “the lower unity.”

To explain in brief: The yichuda ila’ah (the sublime unity) unity is like the bittul of the radiance of the sun within the sun itself, the bittul which characterizes the world of Atzilus, which encompasses one’s entire existence and brings about self-nullification as a matter of course, for one does not feel one’s own identity at all.

Yichuda tata’ah (the lower unity) reflects the bittul of the worlds: Beriah, Yetzirah, and Asiyah, which involves the nullification of self. I.e., one feels that one’s self exists, but understands intellectually that one is butel, for [in truth] one is in the midst of the source which brings one into being, like the radiance of the sun within the sun itself. (All of this, however, is [merely] understood intellectually; it is not felt [consciously].)

The bittul of the sublime unity stems from the perception of its source. When is the source perceived? When the source is not expressed in garments that conceal, despite the fact that it is extended to bring into being and maintain [other existence] — [e.g.,] it radiates forth and causes the world of Atzilus to emanate.

All of this is alluded to in the letter Alef which stands for Alufo shel olam, “the L‑rd of the world.” It is drawn down through the ches that is associated with the sublime Chochmah, the first stage of the chain-like progression within spiritual existence, until it brings into being the world through the daled, the realm of speech. This, however, is referring to speech as it is still bound within its source in thought and indeed, to an even higher level, the speech which exists within its source, i.e., speech as it exists in thought. Therefore the daled [of echad] is oversized.2

The bittul of the lower unity, by contrast, comes about through the awareness that one is in the midst of one’s source even though one does not feel it. This is produced when the source is extended [outward], but as it is extended it becomes enclothed in a garment that conceals. Therefore the created being feels separate [from his source].

[This comes as a result of] the fact that the source (the alef) is drawn down to the lower levels. [This is alluded to] by the letter vav, a line drawn down from above to below (i.e., the alef is exchanged with the vav).

Afterwards, it is enclothed in Chochmah (the ches), but the fundamental enclothement is in the emotional elements of Chochmah, the external elements of the sublime Chochmah. This is alluded to by the letter ayin.3(Thus the ches is transformed into an ayin.)

Afterwards, [influence] is drawn down to bring into being the worlds of Beriah, Yetzirah, and Asiyah through the letters of speech. Since it is drawn down through the external elements of the sublime Chochmah, the power of speech as it is drawn down from its source and inner dimension (the oversized daled) brings into being the actual letters of speech, an ordinary daled. (Thus the oversized daled is transformed into an ordinary daled.)

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See Imrei Binah (Pesach HaShaar, secs.1-7, Shaar Kerias Shema, secs. 70-78); Shoresh Mitzvas HaTefillah from the Tzemach Tzedek (secs. 19, 22, and 38), and the maamar entitled Kol HaMaarich BiEchad, 5678, where [the concepts] are explained in greater detail.