The Rebbe turned the birthday from a celebration into a private Rosh Hashana. On this day, he taught, a person's mazal is ascendant — so it is a day for seclusion, not display: review the year, mend what needs repentance, resolve for the year ahead, give charity before prayer, and learn a maamar. He anchored the modern Chabad observance to HaYom Yom, 11 Nissan.
The observance now taken for granted in Chabad — an aliyah, a chapter of Tehillim, a quiet hour of reckoning, a resolution, tzedakah, a maamar of Chassidus — was, in these letters, being formulated and pressed into practice, letter by letter, anchored to the entry in היום יום for י"א ניסן. The birthday becomes a rung, not an occasion.
The practices he prescribes for the day, by how often each surfaces across the birthday letters.
The heart of it is not the ritual but the התבודדות — an hour alone to review the year that passed and resolve for the one ahead. A birthday, in his hands, is a private Rosh Hashana.
The cultural default is a celebration. He turns the day inward: an accounting of the year, a resolution for the next, added Torah and tzedakah — and all of it "bli blitus," without display. The day is potent, he holds — one's mazal is ascendant — but the potency is spent on reckoning, not festivity. Here, verbatim.