John Gill 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, which have not known [anything] ,
&c.] Of God and of his law and of their duty to God, to their parents, and the rest of their fellow creatures:

may hear, and learn to fear the Lord your God ;
hear the law of God, learn the meaning of it, and so be brought up in the fear, nurture, and admonition of the Lord, and serve him their Creator in the days of their youth:

as long as you live in the land where you go over Jordan to possess
it ;
this being a means to continue the fear, service, and worship of God in their posterity, and so of their long continuance in the land of Canaan.