The four gospels in the New Testament -- Matthew, Mark, Luke, and John -- are our main source of information about the life and teachings of Jesus. But early Christians also wrote some other books about Jesus that didn't get included in the Bible. Old manuscripts of several of these non-biblical books have been discovered during the last century, although in some cases only a fragment of the book has been found. Unfortunately, some other early gospels have been missing since ancient times and could be permanently lost.
But just because an early Christian book was left out of the Bible doesn't mean that it has no value. In fact, some biblical scholars believe that one such book, the Gospel of Thomas, may contain some authentic sayings of Jesus that aren't in the New Testament. Other excluded books may offer some unique insights into the thoughts and views of the first believers. Some of them may also provide valuable information about sects or groups that existed on the fringes of early Christianity.
Several of the rediscovered books belong to a group known as secret gospels. Some of the early Christians thought that these books contained secret knowledge, and only certain people were given the opportunity to read them. In some cases, such a gospel was used by one particular sect of believers, who kept it hidden from outsiders. This secrecy may have been one of the reasons why none of these gospels got into the bible.
Some of the other early books are called Infancy gospels. This is because they contain stories about the infancy and boyhood of Jesus. But most of these stories appear to be fanciful creations rather than descriptions of real events. For this reason, most scholars doubt that this group of gospels has much historical value. Early church leaders must have agreed, because none of these books made it into the Bible.
Gospels that were left out of the Bible are sometimes called non-canonical gospels. The best-known of these are the Gospel of Peter, the Gospel of Mary, the Gospel of Thomas, the Gospel of Judas, and the Gospel of the Hebrews. Actually, some of these books were probably written by anonymous authors who used the names of famous disciples to try to attract attention to their books. For example, the Gospel of Peter probably wasn't written by Simon Peter, but by an unknown person who used his name.
Some scholars think that the Gospel of Thomas was originally a secret gospel. Other secret gospels include the Apocryphon of James, the Secret Gospel of Mark, the Secret Book of John, the Dialogue of the Savior, and the Gospel of Truth.
Early Christian writings contain references to some other lost gospels for which there are no known surviving manuscripts. Actually, it's possible that some of these still do survive, but at unknown locations. Unfortunately, some may be lost forever.
But there also may be hope that some missing books will be discovered in the future, because small fragments of several possible unknown gospels have been found at archaeological sites and other excavations.