Deuteronomy 31:19

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.

Ver. 19. Put it in their mouths.] That out of their own mouths I may judge them; things made up in metre are better remembered. Before the knowledge of letters and writing, among the ancients it was a custom to sing their laws, lest they might forget them; used in the days of Aristotle, by the Agathyrsi, a people near to the Scythians.