Matthew Henry Commentary Deuteronomy 31:1-8

"And Moses went and spake these words unto all Israel. And he said unto them, I am a hundred and twenty years old this day; I can no more go out and come in: and Jehovah hath said unto me, Thou shalt not go over this Jordan. Jehovah thy God, he will go over before thee; he will destroy these nations from before thee, and thou shalt dispossess them: [and] Joshua, he shall go over before thee, as Jehovah hath spoken. And Jehovah will do unto them as he did to Sihon and to Og, the kings of the Amorites, and unto their land; whom he destroyed. And Jehovah will deliver them up before you, and ye shall do unto them according unto all the commandment which I have commanded you. Be strong and of good courage, fear not, nor be affrighted at them: for Jehovah thy God, he it is that doth go with thee; he will not fail thee, nor forsake thee. 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 31:1-8 (ASV)

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. To us this gospel is preached, as well as to them: he will never fail thee, nor forsake thee (Hebrews 13:5).

Moses commends Joshua to them as a leader: one whose wisdom, courage, and affection they had long known; one whom God had appointed to be their leader and therefore would acknowledge and bless.

Joshua is well pleased to be admonished by Moses to be strong and of good courage. Those who have God with them will prosper; therefore, they should be of good courage. Through God let us act valiantly, for through him we will be victorious; if we resist the devil, he will flee from us.