In observing the world in all its intricacy, one finds a general pattern of duplicity throughout creation. Day and night, good and bad, almost all things can be put on a scale between two extremes. Almost everything instinctively falls into one of two categories: that which is uplifting and that which is limiting. In truth, the dychotomy is apparent in the "DNA" of the world itself - the ten Holy Sefiros through which the Creator expressed His Will to "accept", are a delicate interplay between these opposing forces of giving and accepting.
There are two luminaries that hang in our sky, the sun and the moon. The sun gives off light, the moon merely reflects the light of the sun; the day is a time for activity, the night for collecting one's thoughts. As the Jewish Nation was going through transition from Moshe Rabeinu's leadership, which resembled the sun, to Yehoshua's, which resembled the moon, they needed to be reminded that these opposite forces exist only within the context of this world, although they are truly One.
The Parsha starts out with Moshe Rabbeinu's prayer: "Hashem (the Name of Mercy) El-him (the Name of Justice), You (singular, to show that they are one) have begun to show your Greatness (giving) and your Strength (control)" - all the manifestations of Hashem are truly One. He warned them repeatedly: "Lest you raise your eyes and see the sun and the moon... that Hashem put... below all the [upper, heavenly] skies" - you must elevate yourselves above the world of multiplicity. "Know this day and train your heart that Hashem is El-him... there is no other." The Ten Commandments also begin: "I am Hashem your El-him." Although they were given on two tablets, all ten together are one unit. Receiving the torah directly was too much for humans even as exalted as that generation was, and they asked Moshe Rabbeinu to be their conduit to that superhuman Holiness. He became our sun and we were his moon. Yet day and night we are comanded to repeat "Hear O Israel... Hashem is One".
For the Jewish People, the sky is not the limit.
Adapted from Rabbi Vali's book on Dvarim. Questions and subscriptions can be mailed to: the Yeshiva