Deuteronomy — Chapter 31

Take courage and be valiant: fear not, and be not afraid of them: for the Lord thy God himself is thy leader, and will not leave thee nor forsake thee. Moses's valediction to Israel: courage founded on the divine presence, not on human strength. The same promise is renewed to Josue (v. 8), and through him to all who lead God's people.

And Moses wrote this law, and delivered it to the priests the sons of Levi. Moses commits the written Law to the Levitical priesthood as its custodians and interpreters. Lapide draws the parallel with the Church as guardian and interpreter of Sacred Scripture, the successors of Moses in the teaching office.

Now therefore write you this canticle, and teach the children of Israel: that they may know it by heart. God commands the Canticle to be memorised and sung as a perpetual witness against Israel's future apostasies. Lapide (citing Chrysostom): Moses wisely framed the rebuke as a song, so that the sweetness of music would soften the harshness of reproof—the method of the good shepherd who sweetens bitter pasture with the flute.