No one in his right senses denies the authenticity of most of the letters, or epistles, included in the New Testament, and several of these are considerably earlier
documents than the gospels of Matthew, Mark, Luke and John.
The historical value of the Fourth
Gospel is still a matter of debate and uncertainty, but as a historical
document John is clearly less reliable
than the others.
The use by Luke and Matthew of these sources can be demonstrated because, in the case of Mark, the source itself is available, and a comparison of the texts of the three
gospels leaves no reasonable doubt as to its employment in the other two
gospels; in the case of Q, although the original
document has not survived, the occasional verbal agreement in «non-Marcan» passages of Matthew and Luke is such as to show that a
document existed, although its extent can only partially be established and the possibility always remains that more
than one
document was used.