The song of Parshat Ha’azinu is a transition between the first part of Tishrei festivals and the second, between the days of judgement and the days of kindness.
The days between Yom Kippur and Sukkot are ‘half way’ between the first Tishrei festivals and the second. Rosh Hashanah and Yom Kippur are an expression of “His left hand under my head,” while Sukkot, Shemini Atzeret and Simchat Torah are “His right hand hugging me.”
It is the transition between judgement and the left hand under the head, to compassion and the right hand reaching out and embracing, enveloping and allowing us to wholly enter His Presence, “The King brought me into His room.”
Says the “Shem MiShmuel”, Rabbi Shmuel of Sochachov: only the High Priest goes into the Holy of Holies on Yom Kippur, but on Sukkot the whole of Israel enters the all-holy Sukkah, the King’s inner chambers, and “we will rejoice and be happy in You.”
And it is during this period between the days of judgement and the days of kindness, between the Yom Kippur service on the inner altar and the work of Sukkot on the outer altar, we read Parshat Ha’azinu, and make that transition through its song - the transition from great trepidation, introverted contemplation, to the great revelation of Sukkot, moving outside of ourselves and even beyond the borders…
In contrast to Pesach, which emphasizes the difference between the Jewish people and the other nations, on Sukkot we not only pray for them without their knowing, but we even give them an active part in our festivities. Because in the future all nations are destined to go up to Jerusalem on Sukkot, and we even sacrifice 70 cows for the benefit of the 70 nations of the world.
So how does Ha’azinu make this transition?
This is a song that must be written and contemplated “And now write this song for yourselves… and teach it… place it in their mouth…”. Our Sages learned from here that it is a positive commandment for each individual to actually write a Sefer Torah - and this is actually the last of the 613 mitzvot, but Rabbi Tzadok HaCohen of Lublin understood the words differently: “It seems worthy of counting this (contemplating the song) as a mitzvah in itself, and it is a positive Torah commandment.”
Unfortunately, Reb Tzadok did not explain how one should contemplate this song and did not expand. But yes, this song, the mitzvah that concludes the 613, begs contemplation. Let us stop, pause, and think, because it creates the historic continuum with the very first mitzvah, “be fruitful and multiply.” For this is what G-d said to the first two human beings in history: “…be fruitful and multiply and fill the land and subdue it and rule over… every living thing that creeps upon the earth.”
Here we have a simple command divided into two:
The simple understanding is that giving birth to children rescues one from oneself, distracts us from what we take for granted and forces us to come to terms with something beyond us. Forces us to care.
And that is the entire Torah on one leg.
Even this extrication from the ego is not enough though. On Sukkot we also have to leave the home we see as secure, and it is in the gap between these exits that we must embark on the voyage to song. To see life as a creation of “then this song shall speak up.” Not just another day and another day we blindly pass through, but life that is a song - that can respond and talk; a song through which I myself can converse with the story of my own life and listen to its answers and response.
 Song of Songs 2:6.
 Ibid. 1:4.
 Shem MiShmuel, Sukkot, 1918.
 Song of Songs 1:4.
 Deuteronomy 31:19.
 Divrei Sofrim, Kuntress HaZichronot, Third Mitzvah.
 Genesis 1:28.
 Deuteronomy 31:21.