Jesus Inside the New Testament
My Historical Jesus Pick List includes three scholars who do an exceptionally fine job of blasting the use of non-canonical material in historical Jesus research. Two of them are secular liberals, so it's not as if plain sense flows only from Christian bias.
"In recent years we have been witnessing the 'selling' of the apocrypha under the guise of the quest of the historical Jesus. This is a misuse of useful material... What we see in [the agrapha, the apocryphal gospels, and the Gospel of Thomas] is the reaction to or reworking of NT writings by Jewish rabbis engaged in polemics, imaginative Christians reflecting popular piety and legend, and gnostic Christians developing a mystic speculative system. Their versions of Jesus' words and deeds can be included in a 'corpus of Jesus material' if that corpus is understood to contain simply everything and anything that any ancient source ever identified as material coming from Jesus. But such a corpus is the Matthean dragnet from which the good fish of early tradition must be selected for the containers of serious historical research, while the bad fish of later conflation and invention are tossed back into the murky sea of the uncritical mind... For better better or for worse, in our quest for the historical Jesus, we are largely confined to the canonical Gospels." (John P. Meier, A Marginal Jew, Vol I, pp 122-123 140)Negatively, these three writers are in perfect agreement. Positively, however, there is less agreement as to what should be used to derive the Jesus of history. Meier says the synoptics and John; Akenson says Paul, supplemented by the synoptics; and Casey says the synoptics -- coming down hard on John almost as much as the non-canonical gospels. I'm somewhere in between Akenson and Casey. I think Paul is more useful than John in gleaning the historical Jesus; but alongside him and the synoptic writers I would add the underrated epistle of James.
"The most likely way to gain access to the historical Jesus is through the canonical New Testament... Here we enter the world of the big risk. We encounter a particularly aggressive cadre [who] have no tribal name, but 'liberal biblical scholars' is close to being an agreed, if irritatingly undefined label. This is a collection of individuals who place little credence in the direct historical accuracy of the canonical Christian scriptures; yet, in an attempt to jump back into the world prior to the great Destruction, they often embrace a bizarre range of possible pre-70 'gospels'... They are courageous; they have a sense of high intellectual adventure. They are trying to traverse a wide and unchartered ocean in order to find a rich prophesied land on the far side. They long to be able to step off their uncertain and pitching vessel and, even if it's just for a brief time, to their feet on solid land. When they cannot find any, they allow one of their leaders to declare that solid terra is dead ahead, just a few feet, maybe just inches, below the surface. They get to that point, step off, and plunge in far over their heads. The depths, it seems, always overwhelm." (Donald Akenson, Saint Saul: A Skeleton Key to the Historical Jesus, pp 116, 84, 94)
"The major sources for the life and teaching of Jesus are the Gospels of Matthew, Mark, and Luke. It is little short of tragic that I should have had to discuss the historicity of other Gospels... Most of them are Gnostic, or Gnosticizing, documents of much too late a date. They are valuable sources for our understanding the development of Christianity in the second to fourth centuries, but they have nothing to do with the historical Jesus. Some of the falsehoods surrounding them are due primarily to American feminists who wish to believe that Mary Magdalene was a major figure in the ministry of Jesus and in early Christianity. Others are due to pure sensationalism, some but not all of it centering on an American novel [The DaVinci Code]. The last one is a forgery by Morton Smith. In one sense, however, it is fitting that this appendix should end on this note. The major fault of the whole quest of the historical Jesus is that scholars have sought to find a Jesus who reflects their own concerns... this appendix merely catalogues extreme examples of that major fault." (Maurice Casey, Jesus of Nazareth, pp 543-544)