John Gill Commentary Deuteronomy 1:38

"Joshua the son of Nun, who standeth before thee, he shall go in thither: encourage thou him; for he shall cause Israel to inherit it." — Deuteronomy 1:38 (ASV)

[But] Joshua, the son of Nun, which stands before you
His servant and minister, which this phrase expresses:

he shall go in there :
into the good land, instead of Moses, and as his successor, and who was to go before the children of Israel, and introduce them into it, as a type of Christ, who brings many sons to glory:

encourage him ;
with the promise of the divine Presence with him, and of success in subduing the Canaanites, and settling the people of Israel in their land; and so we read that Moses did encourage him, (Deuteronomy 31:7Deuteronomy 31:8)

for he shall cause Israel to inherit it ;
go before them as their captain, and lead them into it; fight their battles for them, conquer their enemies, and divide the land by lot for an inheritance unto them; so the heavenly inheritance is not by the law of Moses, and the works of it, but by Joshua, or Jesus, the Saviour, by his achievements, victories, and conquests.