Albert Barnes Commentary Deuteronomy 31:7-8

"And Moses called unto Joshua, and said unto him in the sight of all Israel, Be strong and of good courage: for thou shalt go with this people into the land which Jehovah hath sworn unto their fathers to give them; and thou shalt cause them to inherit it. And Jehovah, he it is that doth go before thee; he will be with thee, he will not fail thee, neither forsake thee: fear not, neither be dismayed." — Deuteronomy 31:7-8 (ASV)

Moses hands over to Joshua that office as leader of the people, to which he had already been designated (Deuteronomy 1:38; Numbers 27:23). He assigns also to the Levitical priests and the elders, as the ecclesiastical and civil heads of the nation, the responsibility of teaching the law and enforcing its observance (Deuteronomy 31:10–13). Both these were symbolic acts, designed to mark the responsibility of the parties concerned after the death of Moses.