Problem: Deuteronomy records that Moses died before he could enter the land of Israel (Deut. 34). But Moses knew how the Jews had taken possession of the land, which he never saw (v.12). Critics argue that this demonstrates that Moses was not the author of the Pentateuch. Instead, a later author must have composed this work.
Solution: Moses could possibly be speaking about the past conquest in the Transjordan (Deut. 3:12ff), or he could be referring to the future conquest. Since Moses was a prophet of God, he was able to know the future of the nation of Israel. Even if Moses didn’t know the future, he was able to infer the takeover of the Jews based on the promises of God that had already been revealed. Finally, it is also possible that a later writer made a parenthetical note with Moses’ writing. This is why the NASB places vv.10-12 in parentheses. This author was not changing the message of Scripture. Instead, these additions to Moses’ writing help the more current audience understand the message more clearly. This minor historical addition is far from saying that a later author wrote the entire Pentateuch.
“The Horims also dwelt in Seir beforetime; but the children of Esau succeeded them, when they had destroyed them from before them, and dwelt in their stead; as Israel did unto the land of his possession, which the Lord gave unto them. (Deut 2:12)”