Q. Did Moses write the whole Torah at one sitting?
A. The sages of the Talmud (Yoma 37b, Gittin 60a) say that the Torah was given m’gillah m’gillah (“scroll by scroll”), i.e. section by section. According to this theory, the Torah was not recorded at one sitting but in stages.
Nachmanides’ Introduction to Genesis says, “Moses wrote the whole Torah at God’s dictation… When he returned from Mount Sinai, he wrote the first part to the end of the building of the Tabernacle; the latter part was written at the end of the 40 years of wandering in the desert”.
Some things in the first section are worded differently in the second, e.g. the Ex. 20 and Deut. 5 versions of the Decalogue. Dr Aharon Barth points out that this is no argument for different texts by different writers: only the original writer (Moses at God’s command) had the authority to insert a different emphasis the second time.
This whole discussion raises the question of the so-called Higher Criticism of the Bible, which argues that the Torah is a (rather inefficiently) redacted merging of sources from differing times, places and authors. The traditionalist response is that if and where there are difficulties with occasional passages they will be ironed out in God’s good time, but as a matter of principle and logic the Torah is a unitary work, the Word of God put into writing by Moshe Rabbenu. When the critics spoke of a fictitious “R” (Redactor), Franz Rosenzweig said that the “R” was Rabbenu.