“For had ye believed Moses, ye would have believed me: for he wrote of me. But if ye believe not his writings, how shall ye believe my words?”
Numerous passages in the New Testament state that Genesis was written by Moses. But how could Moses have written Genesis? James Ussher, the famous chronologist and historian, dated the Exodus at 1491 BC. Since Moses was about 80 years old at the time, it is likely that he was born about 1571 BC, which equates to 2433 AM (Anno Mundi, years since the creation of the world). Yet Genesis closes with the death of Joseph, about 1635 BC, or 2369 AM. So the last event in Genesis finished 64 years before Moses was born, with over 2,000 years of history to record. Modern historians would turn to earlier writers, but we believe that Moses was inspired by God.
While posing this problem, we must start our answer by acknowledging that we believe what the inspired New Testament writers wrote about the authorship of Genesis. Whatever answer we give must be consistent with that starting point. Scholars fall into error when they allow such questions to cause them to doubt the veracity of Scripture.
It is, of course, possible that Moses received direct revelation from God on what to write down. Another theory, however, which I favor, is that God inspired a number of writers over time to write the various “generations” of Genesis, which Moses then edited under divine inspiration. For example, Genesis 5:1 suggests that the section following was compiled by Adam, while Noah wrote the section starting in Genesis 6:9.
Whatever we believe about HOW Moses wrote Genesis, we accept that he did and that God inspired him to do so.