Be strong and of a good courage, fear not, nor be afraid of them: for the LORD thy God, he it is that doth go with thee; he will not fail thee, nor forsake thee.
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, (Hebrews 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.
Matthew Henry’s Concise Commentary on the Whole Bible
Be strong and of a good courage
The Septuagint version is,
“play the men, and be strong;”
be strong in the Lord, and in the power of his might, trusting and relying on him that goes before you; and so take heart, and be of good courage, and act the manly part; the apostle seems to refer to this passage, (1 Corinthians 16:13) ;
fear not, nor be afraid of them;
their enemies, though so numerous, so mighty, and some of them of a gigantic stature, and their cities strong and well fenced:
for the Lord thy God, he [it is] that doth go with thee:
in comparison of whom, numbers of men, their strength of body, and fortified places, signify nothing:
he will not fail thee, nor forsake thee;
not fail to fulfil his promises to them, not leave them till he had given them complete victory over their enemies, put them into the possession of their land, and settled them in it. This promise, though made to literal Israel, belongs to the spiritual Israel of God, and is made good to every true believer in the Lord; see (Hebrews 13:5).
John Gill’s Exposition of the Bible