Charles Ellicott Commentary Deuteronomy 31:23

"And he gave Joshua the son of Nun a charge, and said, Be strong and of good courage; for thou shalt bring the children of Israel into the land which I sware unto them: and I will be with thee." — Deuteronomy 31:23 (ASV)

And he (Jehovah) gave Joshua the son of Nun a charge. —This is the first record of God’s direct communion with Joshua. He was with Moses on the mount during the first forty days, and departed not out of the Tabernacle when they came down (Exodus 24:13; Exodus 33:11). But we have no note of any Divine communication made to Joshua apart from Moses before this. It ratifies Joshua’s appointment as leader of Israel.

Be strong ... —Compare to Joshua 1:2; Joshua 1:6.