John Wesley on Deuteronomy 31:19

Write this song - Which is contained Deu 32:1 - 43, and is put into a song that it may be better learned, and more fixed in their minds and memories. Put it in their mouths - Cause them to learn it, and sing it one to another, to oblige them to more circumspection. A witness - Of my kindness in giving them so many blessings, of my patience in bearing so long with them, of my clemency in giving them such fair and plain warnings, and my justice in punishing such an incorrigible people.