This is not the post for arguing in favor of any of the metanarratives that frame thinking about Christian origins or, indeed, for their disposal. It’s just a little visual representation of the two most dominant ways of organizing Christian origins.
The first is quite ancient, going back to the mid-to-late second century struggle to define Catholic Christianity over against the schools (“heresies”) that were generally characterized as Gnostic. It continues to find adherents and can be considered the most popular metanarrative.
The other is quite modern and has risen in popularity after the discovery of the Nag Hammadi Library and the Dead Sea Scrolls expanded our knowledge about the variety in both Christianity and Judaism at the turn of the era. The second metanarrative largely agrees with the picture painted above of the second, third, and fourth centuries. The contentious and murky first century of Christianity remains the primary object of speculation and disagreement.
The primary claim of the first metanarrative over against its competitor is that late second century Catholic Christianity represents most faithfully the first century witness to Christianity, which is thus called proto-orthodox (or, traditionally, apostolic). The heterogeneity of Christianity, especially in the form of Gnosticism, is thus claimed to be a secondary development and is dated only to the second century to underscore this.
Another disagreement between the two is the emphasis of the second metanarrative on the continuity of Christianity with its pre-Christian antecedents. Under the first, the story of Christian origins as a series of developments laid on top of the apostolic faith is the emphasis. Under the second, the story of Christian origins is more likely to be told as a story of development from earlier religious and philosophical ideas drawn from Jewish and, sometimes, non-Jewish sources.
While the second metanarrative has started to characterize some writing about Christian origins, it has done so largely by coming out from under the shadow of the first metanarrative. Writers that do not agree with the first timeline above tend to find themselves more in need of justifying themselves to their audience than those who do. It continues to be commonplace to assume the veracity and utility of the first metanarrative in writing about Christian origins.