John Calvin Commentary Deuteronomy 31:13

"and that their children, who have not known, may hear, and learn to fear Jehovah your God, as long as ye live in the land whither ye go over the Jordan to possess it." — Deuteronomy 31:13 (ASV)

And that their children, who have not known anything. Again, we see that their present assembly is not referred to, but that which was to be repeated every seven years, in order that their posterity might be retained in the path of duty. Another use, then, of this recitation is presented: that many who, because of their age, could not be witnesses of the first promulgation, might thereby learn how God was to be served. The possession of the land is again set before them, that God’s bounty may attract them to obedience.