Just because a manuscript is ancient does not mean that it's inspired. There are rumors that say that there are other "gospels" and other "Christian" writings that give alternative views of Christianity that were suppresed and hidden by the church because they challenged ecclesiastical authority. These are the unlying assumption and assertions of many critics and attackers of historic Christianity today, including the Da Vinci Code novel and movie. The thought is that had these other texts been accepted then Christianity would be different than it is now. That much I believe is true.
We live in a culture where the term "Christian" means very many different things to different people. I do not think for a moment that just because a text says it was written by someone who claims to be someone who knew Jesus, or claims to contains the words of Jesus Himself or from God does not mean that the text is "Christian". I put "christian" in quotations because I do not consider them "Christians" because they do not believe or teach what Christians has historically taught. Our Bible has 66 books, and these books that were "excluded" contain information that is contrary to what the 66 teaches. How do we know that they should be excluded?
First, Many of these texts that people use to substantiate the theory that Jesus was married to Mary Magdelene are from this branch of texts. Traditionally, we call these texts psuedographs because we do not know who wrote them and they can only be dated to the second or third centuries AD. Books like the Gospel of Thomas are dated way too late to have been written by the Apostle Thomas.
Second, Many of these texts are referred to as "gnostic". Gnosticism was a sect that believed that Jesus was not human. That there was no physical resurrection. They thought that sin, heaven, and hell are all in the mind. Their Jesus apparently passed on secret knowledge to the disciples. The problem is that most of what they say is contradicted by the Biblical canon.
Third, I defy anyone to show how these "excluded" books fit the defintion of scripture.
All Scripture is God-breathed and is useful for teaching, rebuking, correcting and training in righteousness, so that the man of God may be thoroughly equipped for every good work.
- 2 Timothy 3:16,17
We did not follow cleverly invented stories when we told you about the power and coming of our Lord Jesus Christ, but we were eyewitnesses of his majesty. For he received honor and glory from God the Father when the voice came to him from the Majestic Glory, saying, "This is my Son, whom I love; with him I am well pleased." We ourselves heard this voice that came from heaven when we were with him on the sacred mountain.And we have the word of the prophets made more certain, and you will do well to pay attention to it, as to a light shining in a dark place, until the day dawns and the morning star rises in your hearts. Above all, you must understand that no prophecy of Scripture came about by the prophet's own interpretation. For prophecy never had its origin in the will of man, but men spoke from God as they were carried along by the Holy Spirit. 2 Peter 1:16-21