Erev Shabbat Kodesh
(Excerpts from the Stone Chumash Parshah commentary:)
This is the "Song" of which Moses spoke in the previous chapter. In it, Moses called heaven and earth to bear witness to the calamities that will befall Israel if it sins - and the ultimate joy that will come with the final redemption.
Since the nature of a song is to express recognition of the total harmony of Creation..., it often mixes past, present, and future, for everything is revealed to the prophet as a total reality in which there is no conflict, and in which future and past events are not only in harmony, but clarify one another. Thus everything is melded as if it were all happening at the same time (R' Gedaliah Schorr).
"When He separated the children of man... according to the number of the Children of Israel."
After the Flood, when all people who survived lived together and tried to build the Tower of Babel..., God decided to scatter them. He divided them into seventy languages and separate nations, corresponding to the number of the Children of Israel, i.e., the seventy members of Jacob's family who would later descend to Egypt (Rashi). The connotation is that when the nations at large forfeited their opportunity to be the bearers of God's mission for humanity, He substituted Israel for them and made the number of Jewish families parallel to the number of primary national groups. This illustrates that God ordered history in consonance with the needs of Israel, for it stands to reason that if Jews were to be the ones who would carry out God's designs for history, the conditions of human experience should enable them to do so. As the next verse explains, Israel - His people - is God's portion on earth.