Matthew Henry on Deuteronomy 31:1-8

Moses assures Israel of the constant presence of God with them. This is applied by the apostle to all God's spiritual Israel, to encourage their faith and hope; unto us is this gospel preached, as well as unto them; he will never fail thee, nor forsake thee, Heb 13:5. Moses commends Joshua to them for a leader; one whose wisdom, and courage, and affection they had long known; one whom God had appointed to be their leader; and therefore would own and bless. Joshua is well pleased to be admonished by Moses to be strong and of good courage. Those shall speed well, who have God with them; therefore they ought to be of good courage. Through God let us do valiantly, for through him we shall do victoriously; if we resist the devil, he will flee from us.