Prosper - See the margin. The literal rendering should be retained here since the notion of prosperity is separately introduced by a different word in Joshua 1:8.

Only be thou strong, and very courageous - Ισχυε ουν, και ανδριζου σφοδρα. - Sept. Be strong therefore, and play the man to the uttermost. Though God had promised him that no man should be able to stand before him, yet it was on condition that he should use all his military skill, and avail himself to the uttermost of all the means, natural and providential, which God should place within his reach. God will not have them who refuse to help themselves.

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,

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" (k), 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" (l); the word of God furnishing out instruction to men in every station of life, see Luke 3:10.

(k) "ab so", Montanus, Vatablus, Junius & Tremellius. (l) , Sept. "ut intelligas", V. L. Pagninus, Montanus; "ut prudenter agas", Tigurine version.

Only be thou strong and very courageous, that thou mayest observe to do according to all the law, which Moses my servant commanded thee: turn not from it to the right hand or to the left, that thou mayest {e} prosper whithersoever thou goest.

(e) He shows where true prosperity consists, even to obey the word of God.

1:7 Commanded thee - Remember, that though thou art the commander of my people, yet thou art my subject, and obliged to observe all my commands. To the right hand or to the left - That is, in any kind, or upon any pretence; which plainly shews, that God's assistance promised to him and the Israelites, was conditional, and might justly be withdrawn upon their breach of the conditions. Whithersoever thou goest - That is, whatsoever thou doest. Mens actions are often compared to ways, or steps by which they come to the end they aim at.

prosper: or, do wisely

1:5-9 Joshua is to make the law of God his rule. He is charged to meditate therein day and night, that he might understand it. Whatever affairs of this world we have to mind, we must not neglect the one thing needful. All his orders to the people, and his judgments, must be according to the law of God. Joshua must himself be under command; no man's dignity or dominion sets him above the law of God. He is to encourage himself with the promise and presence of God. Let not the sense of thine own infirmities dishearten thee; God is all-sufficient. I have commanded, called, and commissioned thee to do it, and will be sure to bear thee out in it. When we are in the way of duty, we have reason to be strong and very bold. Our Lord Jesus, as Joshua here, was borne up under his sufferings by a regard to the will of God, and the commandment from his Father.