John Calvin Commentary Deuteronomy 3:21

"And I commanded Joshua at that time, saying, Thine eyes have seen all that Jehovah your God hath done unto these two kings: so shall Jehovah do unto all the kingdoms whither thou goest over." — Deuteronomy 3:21 (ASV)

And I commanded Joshua at that time. He repeats what we have already seen, that he exhorted Joshua, together with all the people, to prepare themselves to occupy the land with alacrity, relying both upon God’s promise and upon the numerous proofs of His assistance, which were so many pledges of the future continuance of His grace.