Room one hundred and fifty in the hall of Hayom Yom.
Monday, 21 Nissan, Shevii Shel Pesach, six days of the Omer, 5703.
First, the Rebbe notes a custom related to the Torah reading of Shevii Shel Pesach: "At the time of the reading of the Shirah, we stand." On this day, we read the Song of the Sea (Shirat HaYam), and during its reading, one must stand.
An interesting nuance: The custom to stand during the reading of the Shirah was already cited in the Hayom Yom of 17 Shevat. 17 Shevat occurs on Shabbat Shirah, when we read the Song of the Sea; we read it twice a year - when Parshat Beshalach, the parshah of "Az Yashir", is read, and on Shevii Shel Pesach. Therefore, the custom of standing appears both on 17 Shevat and here on 21 Nissan.
However, there is a small difference, and seemingly everything is precise. On 17 Shevat, the wording is "We stand at the time of the reading of the Shirah", and here on 21 Nissan: "At the time of the reading of the Shirah, we stand." The content is identical, but the word order is different. I once heard an explanation for the reason for this change: On Shevii Shel Pesach, the essence of the day is the Song of the Sea - this is the miracle that occurred on that day, and in it the essence of the day is encapsulated; in contrast, on 17 Shevat we read the weekly portion, Parshat Beshalach, and the Song of the Sea is found within it.
Since on Shevii Shel Pesach the essence of the day is the Song of the Sea, the Rebbe begins the custom with the words "At the time of the reading of the Shirah" - this is the essence of the day - and what do we do? "we stand." In contrast, on 17 Shevat, which is not the essence of the day, the Rebbe begins in reverse: "We stand" - on this day we stand; and when? Not during the entire Torah reading, but "at the time of the reading of the Shirah." The difference in formulation thus comes to highlight that on Shevii Shel Pesach, the essence of the day is the Song of the Sea.
Shiurim: Chumash, Acharei Mot, Sheni, with Rashi's commentary.
Tehillim, 21st of the month, we say two chapters - chapter 104 and chapter 105.
Tanya, we are in chapter 42 which we began in recent days. The daily shiur is from the word "vehasheinit" on page 118, and concludes on daf 60 with the word "shoma'at etc."
The daily teaching is a custom connected to the night of Shevii Shel Pesach. The Rebbe says: "In Lubavitch, they stayed awake on Shevii Shel Pesach, and also on Shavuot and Hoshana Rabbah." In Lubavitch, the custom was to remain awake on the night of Shevii Shel Pesach, and also - as he adds - on the night of the festival of Shavuot and on the night of Hoshana Rabbah.
In one of his sichos, the Rebbe Rayatz mentions that in Lubavitch, there were nights when they did not recite the "Bedtime Shema", because they did not go to sleep at all. There he details these nights - as he notes here, but slightly more: the night of Shevii Shel Pesach, the night of Hoshana Rabbah, and the night of Shavuot - the three days mentioned here as well; and there he also adds the first night of the festival of Pesach.
It is interesting that at the meal of Shevii Shel Pesach 5729, when the Rebbe sat with the crowd at the meal in the apartment of the Rebbe Rayatz, they asked the Rebbe why in the Hayom Yom of 21 Nissan he omitted the first night of the festival of Pesach when he listed the nights on which they stayed awake in Lubavitch - since in the sichos of the Rebbe Rayatz it also appears as one of the four nights. The Rebbe answered that this is how the Rebbe Rayatz instructed to print the custom on this day. And as we have seen that every detail here is precise, so the Rebbe Rayatz said to include only these three, and not to practically include the first night of the festival of Pesach in the custom.
Let us look at the continuation of the teaching. The Rebbe Rayatz says: "Since I was nine years old, I have not gone to my bed on Shevii Shel Pesach" - already at age nine, as a child, he was awake on the night of Shevii Shel Pesach. And he concludes: "One should learn the entire night."
It should be added, that on Pesach 5735, the Rashag, the son-in-law of the Rebbe Rayatz, asked the Rebbe: staying awake on the night of Shavuot and on the night of Hoshana Rabbah appears in the Shulchan Aruch, but the custom to stay awake on the night of Shevii Shel Pesach, cited here, does not appear in the Shulchan Aruch - and what is its source? From where is the custom that in Lubavitch they stayed awake on the night of Shevii Shel Pesach? And the Rebbe answered him that the source is the words of the Rebbe Rashab n.e.; this is the source from his perspective, and this is how it should be.
Regarding the night of Shavuot mentioned here, the Rebbe Rashab writes that he found a holy manuscript of the Mitteler Rebbe, that for someone who is awake on the night of Shavuot, very lofty matters shine - as also appears here in the daily teaching. In any case, what is relevant to this day is the night of Shevii Shel Pesach, as this is the teaching for 21 Nissan, Shevii Shel Pesach.