This is the meaning of what Moshe Rabeinu said: “You have seen the great miracles that Hashem has done for you in Egypt and in the desert.” Meaning, until now you were the ones seeing, through your own effort of creating an “awakening from below.”
However, as Moshe continued to say: “Hashem has not given you a heart to understand or eyes to see...until this day.” Meaning, they did not yet have the level of a “pure heart” that is given from Above, since no created being can attain this level using only its own initiate.
This was the idea of eating the (supernatural food called) Munn, as it is written, “He (Hashem) afflicted you and made you hungry, and He fed you the Munn.”
Even though the Munn was very tasty, it had two discomforting aspects: 1- it looked unappetizing, 2- it couldn’t be stored from one day to the next. Because of this, eating the Munn took away some of the attraction to food and materialism, and promoted trust in Hashem to provide a person each day with his sustenance. The purpose of eating the Munn was thus to humble the people and enable them to connect to Hashem better.
Meaning, that through the Munn, and through other humbling things and discomfort, they merited to receive a much higher level (of love and fear of Hashem), and were able to receive the level of “a pure heart.”
This is similar to the concept of “fasting” during the Ten Days of Teshuva.
This is why we read this Parsha (Torah Portion), i.e., Ki Savo, that contains the passages of “the Curses,” before Rosh Hashana.
Before Rosh Hashana (and Shavuos) we read in the Torah about the punishments Hashem said He will bring upon those who abandon Him and worship idols etc. These passages in the Torah are called “the Curses.” The Gemara (Megilla 31b) says that this is done so that we may “finish off the curses of the year.” Meaning, that if Hashem decreed any bad things in the coming year, it should be fulfilled by reading about it, and not by it actually happening in the physical world.
Tosfos (there) explains that we read the curses the second to last week of the year, which is always Parshas Ki Savo, so that the Parsha right before Rosh Hashana, Parshas Nitzavim, will contain only blessings.
The Alter Rebbe is explaining another idea behind reading the curses before Rosh Hashana. Since on Rosh Hashana we have the opportunity to receive a much deeper connection to Hashem than we ever had before, we need to refine and humble ourselves, so that we will be receptive to this new level of connection. One who feels self-satisfied and complete in himself will not be yearning for a new and deeper connection to Hashem. That is why we read about the punishments: In order to humble us, so that we may grow in our connection to Him.
This is similar to the story of the Jewish People in the Desert. While they were in the Desert, they served Hashem on a certain level, with a certain degree of love and fear of Hashem. But before they came into the Holy Land, they needed to receive from Hashem a totally new level of connection to Him, a deeper level of love and fear of Him. (This deeper connection was needed to empower them to handle the challenges of settling the physical land without getting distracted from their spiritual purpose.) This deeper level could only be given to them as a gift from Above. In order for them to be able to receive this gift from Above, they needed to be humbled and refined. This was accomplished by wandering in the desert for forty years and going wherever Hashem guided them, and by eating only the Munn that Hashem gave them for each day. After forty years of refinement, they were finally ready to receive a new and deeper level of connection to Hashem, a higher level of love and fear of Hashem.
In other words, during the forty years in the desert, the Jewish People “saw” Hashem’s wonders and inspired themselves with that knowledge to connect to Hashem. However, at the end of the forty years, Hashem gave them “a heart to understand, eyes to see, and ears to hear,” i.e., an awareness and feeling for Hashem, on a totally different level than they would ever be able to attain through only their own effort.
This is similar to how we work the entire year, and especially in Elul and Tishrei, to come to an awareness and feeling for Hashem, and to humble and refine ourselves, so that on Rosh Hashanah and the other Ten Days of Teshuva, we can receive from Hashem an incomparably deeper and higher level of connection with him.
