Moses didn't write any of the Bible?
There's nothing new about this assertion, but I want to address it here as I recently heard the statement 'Moses did not write any of the Bible' from the pastor of a church (not my own church) which regards itself as broadly evangelical. Does this denial really matter? I think it does, read on for the reason why.
The traditional view has been that Moses wrote what's called the Pentateuch, or the first five books of the Bible. It is important to always test such claims by examining Scripture itself, as the Bereans did (Acts 17:11), so the issue of whether Moses wrote any of Genesis to Deuteronomy is not to be ultimately settled by appeals to tradition, what we need to consider is what does Scripture itself claim on the matter.
Bear in mind that many Bibles include descriptive titles of each book, as well as paragraph headings throughout the text, etc. They can be a convenient way of finding your way around, but these descriptions or summaries do not come from the original text - the translators have added them. The actual Scriptural text is the chapter and verse text (the chapter and verse numbers were also added for ease of reference, they were not in the originals).
Where Scripture leaves a question unanswered, it's ok to say, 'we don't know'...
There is definitely freedom to say 'we don't know' where Scripture itself does not give us an answer to some question we might have. For example, we don't know who wrote the New Testament letter to the Hebrews. All kinds of theories have been presented, and there's nothing wrong with scholarly debate and research into the question. It's a fascinating question. And the question is open because Scripture has left it open.
...but where Scripture gives a clear answer, it's dangerous to disagree
Scripture is God's word to us. There are serious implications to not believing what God says about anything.
So what are the implications of saying Moses wrote none of the Hebrew Scriptures at all? Why does that matter? Read on...
The books of Genesis to Deuteronomy are part of the word of God
If any of the words of the first five books were written by someone other than Moses, whoever wrote them was most certainly divinely inspired, and those books are a part of the canon of Scripture, the word of God. I don't have a problem with saying that Moses himself didn't necessarily write every word of all of those books, as, to the best of my knowledge, the Scriptures do not claim anywhere that he did write every word in all of them. The last chapter of Deuteronomy contains an account of Moses' death - I don't believe Moses wrote that himself! Some people have argued that Moses did write, prophetically, about his own death. Well, God could have inspired him to do that, if he wanted to. But the Scriptures don't make the claim that he did.
...but there is a serious problem with saying Moses wrote none of it
The serious problem with saying Moses did not write any of the first five books of the Bible is that Scripture directly attributes much of it to Moses' authorship. And, most significantly of all, Jesus himself tells us that Moses wrote at least certain parts of those books.
I will focus here on what Jesus had to say about Moses' authorship of Scripture. My reason is this: if Jesus said that Moses did write at least part of the Hebrew Scriptures, then if we say Moses did no such thing, we are either saying that the gospels do not accurately record what Jesus actually said (which has enormous implications for what we believe about everything else in the gospels), or we are saying that Jesus' words do not mean what they clearly say, or that Jesus was mistaken, or confused, about what he was saying. Jesus is the eternal Son of God! The Author of life! He was not, and is not, confused or mistaken about anything, and any suggestion that he is, quite frankly, would be blasphemous.
What did Jesus say about Moses' authorship of any of the Hebrew Scriptures?
"For if you believed Moses, you would believe me, for he wrote about me. But if you do not believe what he wrote, how will you believe my words?"
Jesus' statements that 'Moses wrote about me', and 'if you do not believe what he wrote...', seem conclusive to me.
Another example of Jesus' view of whether Moses wrote any of the Scriptures
In Mark 10 there's an account of Jesus being asked a question about divorce. Jesus invited the Pharisees to repeat what they knew of what the Mosaic Law had to say on the subject. The Pharisees' response, and Jesus' comment on it, are references to Deuteronomy 24:
There came to him [Jesus] some Pharisees, who tested him by asking, "Is it lawful for a man to divorce his wife?"
Do you believe what Jesus himself said or not?
There are many other arguments that could be presented from Scripture for Moses as the author of much, if not all, of Genesis to Deuteronomy. But I really don't think they need presenting - what Jesus had to say settles the matter. If we don't think Moses wrote any of Genesis to Deuteronomy, and if we know what Jesus said on the matter, then either we think the gospels are not reliable accounts of what Jesus said, or we think that Jesus' words do not mean what they say, or we think that Jesus was mistaken. All three of these stances are extremely dangerous.
The Bible does not directly assert that in order to be saved, in order to become a Christian, we must believe that Moses wrote the Pentateuch. But once we are aware of what Jesus said on the subject, then there are serious implications for believing that Moses wrote none of it. A true believer recognises the Bible as God's word, and trusts what Jesus had to say on every subject, because of who he is.