John Calvin Commentary Deuteronomy 31:7

"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." — Deuteronomy 31:7 (ASV)

And Moses called unto Joshua. It therefore appears that those who are entrusted with a public charge need a twofold confirmation. For, after addressing a general instruction to all the people, he directs his words specifically to Joshua himself, as to one whose task it was to set an example of bravery for others, and for whom severe contests awaited.

Since, then, it is more difficult to lead everyone else than to follow a leader, it is necessary that he who is set over many should far excel them. But, since no one can do anything by himself, we must seek from God whatever we need. Therefore, what Moses had commanded the whole people, he now repeats to a single individual, because the burden of ruling them was placed upon him.

This must be observed more carefully because, in proportion to the degree of honor in which a man is placed, he tends to look down disdainfully upon all admonitions. From this it happens that those who are prominent in the world carelessly reject the exhortations of God’s servants. But Moses thoroughly overthrows all such arrogance when he shows that all who are in authority should not only be instructed together with others but even be pressed more urgently.

When Moses, here and previously, forbids believers from giving way to fear or dread, it must be observed that he does not intend for them to be entirely devoid of feeling, hardened into indifference to every danger. Nor does he want them to suppose, as some madmen do, that bravery requires stupidity. Instead, he would have them be possessed of such confidence as can overcome all fears that impede the course of their calling.

The Apostle appropriately extends this lesson further where he wishes to correct greed, which arises from excessive anxiety, while miserable people do not sufficiently reflect on what it means to have God as their perpetual helper (Hebrews 13:5).