Only be thou strong, and very courageous
For though Joshua was a man of valour and courage, as appears by his war with Amalek, yet there was need of this exhortation, and of repeating it, since he was to engage with a people more and mightier than those with him, and who dwelt in strong and fortified places, and had been preparing for some time, having had notice, and were in expectation of the Israelites' attempt upon them:
that thou mayest observe to do according to all the law which Moses my
servant commanded thee;
not only as a private man obliged to observe the whole law, and act according to it in all things; though no mere man is capable of it, only Joshua's antitype, who is the end of it for righteousness to all that believe, having fulfilled it in all respects; but as the supreme magistrate under God, who was to see that the law was obeyed by the people in all things, and particularly as the general of the army, who was to observe to do what had been ordered, with respect to the Canaanites, see ( Deuteronomy 7:1-5 ) ;
turn not from it [to] the right hand or [to] the left:
from the law, by adding to it, or taking from it; so Ben Gersom explains it,
``turning to the right hand is, when any adds to its words; and turning to the left hand, when he diminishes from them;''or "from him" F11, that is, from Moses; from his good way, as Kimchi; though he adds, or else from the book of the law; for though he does not mention the book, he does the law; so Ben Melech:
that thou mayest prosper whithersoever thou goest;
succeed in every battle he engaged in; it would be well if generals of armies would observe this; the way to obtain victory over enemies being to be observant of the laws of God themselves, and to take care that they be observed by the soldiers under their command: or "that thou mayest act wisely" F12; the word of God furnishing out instruction to men in every station of life, see ( Luke 3:10-14 ) .