This is connected to the meaning of the verse (Tehillim 100:3), “He made us and ‘לֹא-not’ we ourselves,” it is read ‘לוֹ-to Him’ with a ו', but it is written ‘לֹא-not’ with an א'.
In the 24 Books of Tanach there are many words that are written one way and we have a received tradition that they are read differently. The difference in meaning here is as follows: With the word לֹא with an א' it means, “He made us, and not we ourselves.” But, with לוֹ with a ו' the meaning is, “He made us and we are His [nation].”
Chapter 4
To explain this idea: How is it that we can be “His nation” by connecting to Hashem through His revelations in the levels of Histalshelus?
It is only because “He made us and He used “וְלֹא” – with an א' – which is the level of Kesser.
By substituting the letter ו' with the letter א', the verse implies that “וְלוֹ - and [we are] His” because of the letter א', which represents Kesser, i.e., we are His people in Mitzvah performance because of the level of Kesser that is revealed in us.
The Mittler Rebbe explains that the letter ו' represents the 6 attributes of Ze’eir Anpin, and the substitution with the letter א' represents bringing down Kesser into Ze’eir Anpin, which then comes into the souls of Avram’s descendants, enabling them to fulfill mitzvos.
Because the letter א' is the ‘head,’ i.e., source, of the letters, corresponding to Kesser, the ‘head’ and source of the sefiros. Through this level, we can be ‘לוֹ-His” with a ו', that “we are His nation.”
Because since this level is above Hishtalshelus, it can radiate even down ‘below’ Hishtalshelus.
And therefore, when the Torah was given and the mitzvos were commanded to be performed in actual deed, the first mitzvah begin with the letter א': “אָנֹכִי-I am Hashem who took you out of Mitzraim.”
Because, for the mitzvos to be fulfilled in action and affect Unifications Above through action requires that an illumination from the level of Kesser be revealed.
Therefore, the first mitzvah begins with א', corresponding to Kesser, a ray shining from the “White paths of Kesser,”
As explained above, this refers to the Essential Will of Hashem, which transcends and is the source of the sefiros of Atzilus. This level, which is the source of Mitzvos, is represented by the letter א', which is the ‘head’ and source of the letters.
