Scholarly opinion is generally that the three synoptic gospels (Matthew, Mark, and Luke; called “synoptic” to mean “viewed together”, comparable) used a single source document that has not survived, called “Q” (from the German Quelle = source).
The earliest New Testament texts are, in fact, some of the letters of Paul. Matthew, Mark, and Luke come later.
The idea is that the earliest followers of Jesus expected his Return at any moment, followed by a Messianic Age of Heaven on Earth. So the stories about Jesus and his teachings were all oral – no need to bother writing things down, when he would be here soon to tell us all again. As the original generation died out, however, there was a desire to set things down in writing.
There are great similarities among the the synoptic gospels. This was traditionally explained in terms of having roots that extended back independently to a common apostolic witness: they all drew from the same information.
However, most scholars today are convinced that there is a direct literary dependency. The theory is supported by:
- common subject matter
- correspondance of sequence and continuity of events
- similar sentence and word order
- extensive vocabulary agreement, and use of the same harsh grammatical constructions or unusual words.
Of over 600 verses in Mark’s narrative, 90% are in the Gospel of Matthew and 50% are in the Gospel of Luke. The outline of Mark’s narrative is almost entirely reproduced by the other two synoptic gospels, with Luke corresponding to the early part of Mark’s sequence, and Matthew to the later.
In the sections of Matthew that relate the same tradition as in Mark, the use of the same words is over 73%. Luke used about 66% of Mark’s words. The end-time discourse of Jesus shows large blocks of material that are word-for-word the same (Mark 13:5-8, 14-17, 28-32, and parallels.)
The evidence goes on, and I suggest Keith Nicle’s THE SYNOPTIC GOSPELS if you are interested. The hypothesis is an initial document called Q, which ceased to circulate independently and fell into disuse in the early church, once it had been incorporated into Matthew and Luke. It is possible that the community responsible for writing Q also held opinions that were later regarded as heretical, and so was rejected from the early church. Mark is NOT assumed to have copied from Q, but Matthew and Luke copied from both Q and Mark.
Some scholars assume Q was a single document. Others use Q as a symbol of convenience, asuming several sources of material present in Matthew and Luke but not in Mark. It is not possible to reconstruct the exact contents of Q, but most scholars believe it is primarily the speeches and sayings attributed to Jesus (exceptions are brief references to John the Baptist, the temptation in the wilderness, and the centurion at Capernaum.) Because Matthew and Luke record the same sayings of Jesus in a different context, the assumption is that Q was a collection of the sayings without any narrative description of the circumstances surrounding the saying.
Q presumably contained no Passion narrative and lacked any reference to the cross. Thus, one thinks of it not as a gospel but as a collectionof miscellaneous sayings, reporting the teaching and preaching of Jesus. This was used by Matthew and Luke to augment Mark’s narrative, which puts more emphasis on the mighty acts and miraculous deeds of Jesus, than on his teachings.a
OK? That’s the nutshell version.