The Gospel of Thomas is the noncanonical gospel par excellence. It has been studied more than all the other noncanonical gospels put together, and for good reason. Among all of the extant gospels that did not make it into the New Testament canon, this is the one that has the best claim to antiquity, the only one that provides the potential for extended reflection on the sayings of the historical Jesus. However much we may wish to draw attention to the importance of understanding the development of Christianity in the second century, reaching back into the first century is still far more attractive to most historians of Christian origins. There is romance in the idea that this text, so recently discovered, could provide a special witness to the earliest phase of Christianity.
For many, the text takes its place in a dynamic early Christian world in which variety and diversity are the chief characteristics. Words like “orthodoxy” are firmly out of favor. Talk of “Christianities” is in. Indeed, the discovery of the Gospel of Thomas provided a catalyst for the development of this perspective in which it now plays such a major role. The impetus for this new approach, in some senses its manifesto, was Trajectories through
Early Christianity by James Robinson and Helmut Koester, first published in 1971. The book was in part a development of and in part a reaction to Rudolf Bultmann’s views, now packaged for a new era. Early Christian diversity looms large, and newly discovered early Christian texts take their place in a world of competing trajectories. The Gospel of Thomas, unavailable in full to Bultmann when he was writing his seminal History of the Synoptic
Tradition, now rises to new prominence alongside the hypothetical source Q, as two early witnesses to a passion-free, sayings-based trajectory in early Christianity, which contrasted with the passion-centered, Pauline influenced versions of Christianity that later won the day.
Trajectories has influenced a generation of scholarship on Christian origins, and its legacy is perhaps most pronounced in the key contributions of scholars like Robert Funk and John Dominic Crossan, most famous for their prominence in the Jesus Seminar, who have applied a model that prioritizes Q and Thomas in historical Jesus research. The responsible historical Jesus scholar now works outside canonical boundaries, and those who ignore texts like Thomas are chastised for their canonical bias. They are seen as engaging in a kind of stubborn, confessional attempt to skew the field by ignoring much of the best evidence.
(Thomas and the Gospels: The Case for Thomas's Familiarity with the Synoptic Gospels (Grand Rapids: Eerdmans, 2012), 1-2)