It contains only 43 verses, yet the song Moses taught the Jews on the last day of his life spans all of Jewish history, from the very beginning when “He found them in a desert land,” all the way to the future redemption when the nations will praise G‑d, “For He will... appease His land [and] His people.”
In the opening phrase, Moses calls for heaven and earth to bear witness:
"Give ear, O heavens, and I will speak! And let the earth hear the words of my mouth!"
Because Jewish law requires legal matters to be established on the basis of two witnesses, Moses called upon both heaven and earth to bear witness that he indeed had conveyed this song to the people.
The testimony of heaven and earth is more than merely a poetic metaphor. Moses was conveying the profound lesson that in order for the message to endure, the Jew must evoke both heaven and earth.
The purpose of the Jewish people—the objective of all Jewish history—is the marriage of heaven and earth. While many spiritual seekers and virtually all religions seek to escape the confines of the flesh and climb heavenward, the Jew is charged with a far more profound calling: first create peace, then build a bridge, and finally marry heaven and earth.
Moses uses different words to address the heavens and the earth. He says: “Give ear, O heavens (Haazinu), and “let the earth hear” (va’tishma). The Hebrew word haazinu, give ear, is used specifically when the listener is in close proximity to the speaker. The word tishma, hear, however, applies to hearing something distant. Indeed, the Midrash explains that Moses was close to the heavens—i.e., spirituality was the reality of his existence. Hence he employed the word haazinu when addressing the heavens. The material world, however, was distant and insignificant to Moses, so he used the word tishma when addressing the earth.
Moses was close to the heavens, but since the purpose of Judaism is to connect both matter and spirit, Moses had to invoke not only heaven but earth as well.
We each have a “heaven” and “earth” within us. Part of us seeks the transcendent and the spiritual, while another part is drawn to the earthly and the physical. Perhaps more than any other part of the song, the opening words, “Give ear O heavens” and “Let the earth hear,” capture the mission of the Jew.
The song is read on Shabbat in close proximity to the holidays of Yom Kippur and Sukkot, for Yom Kippur and Sukkot are the embodiment of the song. On Yom Kippur we reach to the heavens, we connect to the core of our soul and feel unified with G‑d. But, just as we reach the climax of the holiness of Yom Kippur, we transition to preparation for the holiday of Sukkot, when we celebrate the physical bounty with which we have been blessed:
You shall make yourself the Festival of Sukkot for seven days, when you gather in [the produce] from your threshing floor and your vat… Seven days you shall celebrate the Festival to the L‑rd, your G‑d, in the place which the L‑rd shall choose, because the L‑rd, your G‑d, will bless you in all your produce, and in all the work of your hands, and you will only be happy.
The combination of Yom Kippur and Sukkot represents the life of the Jew. We are “close to heaven,” we connect to our angelic, spiritual, and pure soul on Yom Kippur, and then we connect that spiritual awareness to the field, to sanctify and uplift the blessings of everyday life.
-adapted from www.chabad.org