If Moses wrote the first five books of the Bible, how did he write about his own death in Deuteronomy 34?

When Moses completed his writings and turned over the Book of the Law to the Levites, he handed them a single scroll.(1) It contained what would later be called the Pentateuch—Genesis, Exodus, Leviticus, Numbers, and Deuteronomy. To the Jews, this collective work would be known as the Torah. Presumably, Greek translators were the ones who later divided Moses’s writings into the five separate works we have in our Bibles today and gave the books their individual titles.(2)

It’s possible that God could have instructed Moses beforehand on what to write concerning his own death. However, it seems more likely that Joshua wrote the last bit of Deuteronomy. As God’s appointed successor to Moses, it would have been fairly easy for him to access the scroll and add this portion to the end. Moreover, Moses’s obituary is not written from a personal viewpoint and doesn’t sound like something Moses would write about himself. The tone of the writing is one of great respect toward Moses. The wording is much more in keeping with how Joshua would later refer to Moses in his own book, particularly in calling him “the servant of the Lord.”

Footnotes:

(1) See Deuteronomy 31:24–26 for the account of Moses handing his book over to the Levites.

(2) For more information, see “Pentateuch” in Smith’s Bible Dictionary and in Easton’s Bible Dictionary.