Did Moses write the first five books of the Bible?
The Baha'i writings and the Quran affirm the Divine origins of both the Torah and the Gospels and they were Revelations from Moses and Jesus. Both sets of writings do not specify who wrote the books.
Scholars believe the Torah was first written down during the Babylonian exile and refer to multiple authors. They are in agreement that the Gospels were all initially written down within the first century of Christ's ministry but are unable to agree on the actual authors.
Did Jesus really say the things that the gospel writer say he did?
The Baha'i writings say we can not know if the Gospels record the exact words Jesus used. However the books are protected by God and convey all that God wished to. Scholars (even atheists) agree that Jesus was baptised and crucified.
Jesus and Moses are the ones that received the divine revelation. If they aren't the ones that wrote it down, then that how can we and why would we assume the information is correct?
The Quran and Baha'i writings are authentic.
We both have talked about the gospels being second or third hand information. Christians say that Matthew and John were eyewitnesses and Luke and Mark were with the apostles and heard the stories from them.
There is no agreement from scholars about the authorship of the gospels.
But there are even more hands involved in the transmission of the message, angels. How do we know that a spirit being appeared and told anybody anything? How do we know that such a being was authorized by God to pass on some information to a human, who then passed it on to the rest of us? Talking to angels can easily be faked and could be used to give some "supernatural" source for some spiritual ideas the person has. So what is "divine" revelation anyway? Can we trust the people that wrote that some other person, like a Jesus or a Moses, spoke with God or spoke with an angel?
There is no way of verifying whether or not Moses, Muhammad, Christ or Baha'u'llah had an experience with angels other than their testimony. The argument that whether each revelation is Divine or man made is at the heart of many of the debates on this forum.
People do put their trust in those things written. But then comes the problem of interpreting what it all means and how to put it into practice. So we have words that people trust as being the truth that tells them that they have accumulated bad karma and must do certain things to get rid of it to get out of the birth and rebirth cycle. We have other people that trust their words that tells them that the first humans sinned, and because of that sin, all humans are born with a sin nature, or even worse, they are tainted with "original" sin. Their religion tells them what to do to get right with God. Part of that is to accept that God sent his son to die for them to pay the penalty for that sin. That he was sinless and was a perfect sacrifice. And you know how that story ends up. That person was killed but was said to have come back to life and floated up into the sky to be with God.
So beyond whether or not each of these Abrahamic Faiths is Divinely inspired the next question is that of interpretation.
What we chose to believe and have faith in is one of the most important questions for each of us.