Almost all of Ha'azinu is a song, written in the Torah in two parallel columns. Moshe summons the heavens and the earth to stand as eternal witnesses to what will happen if the Jewish People sin and do not obey the Torah. He reminds the people to examine the history of the world, and note how the Jewish People are rescued from obliteration in each generation - that Hashem "pulls the strings" of world events so that Bnei Yisrael can fulfill their destiny as His messengers in the world. Hashem's kindness is such that Israel should be eternally grateful, not just for sustaining them in the wilderness, but for bringing them to a land of amazing abundance, and for defeating their enemies. But, this physical bounty leads the people to become self-satisfied and over-indulged. Physical pleasures corrupt the morals of the people. They worship empty idols and powerless gods, and indulge in all kinds of depravity. Hashem will then let nations with no moral worth subjugate Israel and scatter them across the world. However, their only purpose is as a rod to chastise the Jewish People. When these nations think that it is through their own power that they have dominated Israel, Hashem will remind them that they are no more that a tool to do His will. The purpose of the Jewish People is fundamental - that man should know his Creator. Neither exile nor suffering can sever the bond between Hashem and His people, and eventually in the final redemption this closeness will be restored. Hashem will then turn His anger against the enemies of Israel, as though they were His enemies, showing no mercy to the tormentors of His people. Hashem then gives His last commandment to Moshe: That he should ascend Mount Nevo and be gathered there to his people.
This is the first Shabbat of the year. It is the prototype, the blueprint for the whole year. Because of this, we must be especially careful to guard its sanctity. The Talmud tells us that if the Jewish People had kept the first Shabbat properly, no nation could have ruled over them.
On Rosh Hashanah a new order is created for all the days of the year. Thus if the first Shabbat of the year is correctly observed, then the whole year follows suit.
Man was created on Erev Shabbat, on Friday afternoon, in order that he could immediately enter straight into Shabbat. But before Shabbat came, Man had already sinned.
Shabbat is an aid to teshuva. As our Sages teach (Berachot 37), a tzaddik gamur (completely righteous person) cannot stand in the place of a ba'al teshuva (someone who returns to Judaism).
Tzaddikim uphold the world, as it says in Proverbs "The tzaddik is the foundation of the world," but "teshuva preceded the world" (Pesachim 54) so the level of the ba'al teshuva is before the world and above the world.
Just as the ba'al teshuva is before the world, and thus above it, so too Shabbat has a radiance which is higher than the seven days of the week - a reflection of the world to come.