Gregory's article is important because it provides a clear critique of Edwards's own earlier work on the Hebrew Gospel, "The Gospel of the Ebionites and the Gospel of Luke," NTS 48 (2002): 568–86. In the article, Gregory argues persuasively that the Gospel of the Ebionites, as witnessed in quotations in Epiphanius's Panarion, is best understood on the consensus theory that it is a post-synoptic harmony, against Edwards's theory that it is one of Luke's sources. Now in Edwards's book, Gregory's article is given scant attention. Rather than engaging with Gregory's critique of his earlier work, Edwards deals with it in a footnote to the following effect:
In response to my article . . . . Gregory . . . seems to concede 1) that all but two of the excerpts of the Gospel of the Ebionites that are found in Epiphanius are more closely related to Luke than to any other Gospel, and 2) that the Lukan parallels usually appear in Luke's single tradition (349). Gregory dismisses the weight of this evidence, however, and in a chain of reasoning that is neither entirely clear nor compelling concludes that the Hebrew Gospel was a compilation from Luke and the other Synoptic Gospels (p. 66, n. 65).Edwards's 1) and 2) here are poor summaries two sentences in Gregory's article to the following effect:
Of the seven excerpts of the Gospel of the Ebionites that are found in Epiphanius, five include details that are paralleled in Luke. As Edwards notes, many of these parallels come from Lukan single tradition.In other words, Gregory points out that "five [passages] include details that are paralleled in Luke", which is quite different from saying that they are "more closely related to Luke than to any other Gospel". Gregory's comment that "many of these parallels come from Lukan single tradition" does not translate into "the Lukan parallels usually appear in Luke's single tradition".
Aside from the misreading, it is disappointing that Edwards does not take Gregory's critique seriously. It is not the case that Gregory's reasoning is "neither entirely clear nor compelling". On the contrary, Gregory applies the well-established criterion of looking for evidence of Matthew's and Luke's redactional activity in the material that is paralleled in the Gospel of the Ebionites. The point of this kind approach, which is common in discussions of the relationships between Gospels, is that the presence of redactional activity signals use of the Gospel in question rather than its source material.
