Deuteronomy 31:19 - Clarke's commentary and critical notes on the Bible

Now therefore write ye this song for you, and teach it the children of Israel: put it in their mouths, that this song may be a witness for me against the children of Israel. Write ye this song - The song which follows in the next chapter. Things which were of great importance and of common concern were, among the ancients, put into verse, as this was found the best method of keeping them in remembrance, especially in those times when writing was little practiced. Even prose was sometimes sung. The history of Herodotus was divided into Nine books, and each inscribed with the name of one of the Nine Muses, because these books were anciently sung. Homer is reported to have sung his poems through different Greek cities. Aristotle observes that anciently the people sung their laws. And Cicero observes that it was a custom among the ancient Romans to sing the praises of their heroes at the public festivals. This was the case among the northern inhabitants of Europe, particularly in Ireland and Scotland; hence the Gaelic poetry of Ossian and others. See Dodd; and see the note on Exodus 15:1, where the subject is largely treated.