If I may push back a little bit. I'm not sure that such a sounding of trumpets was ever necessary. Such statements go back a few more decades:
From the 1825 translation of Winer, page 102 wrote:the aorist marks simply past time, and is the usual tense of narration; the imperfect and pluperfect are always used in reference to a secondary or subsidiary action or event, which is past, but which stands connected in respect to time with the main action or event; while the perfect expresses past time in connexion with the present.
The specific language used by Bently Layton is different from Winer and reflects the language used by students of R. E. Longacre, see The Routledge Linguistics Encyclopedia
edited by Kirsten Malmkjaer, (no page #) try google: "main line" narrative longacre, should get you there. Also over 3,000 hits on textlinguitics related sources.
Another search: "jesus is on the main line" longacre, produces only one hit, Full text of "Minutes of the Seventy-Seventh Annual Assembly of the Disciples of Christ of the Washington-Norfolk District in Eastern North Carolina and Virginia"
My point: Bently Layton is introducing concepts (topic marking, main line, background) into his presentation that are standard fare in the textlinguistic literature of the last three decades of the 20th century. I am not claiming that these ideas were never addressed before that. But the specific terminology used sounded familiar. I read Longacre's Grammar of Discourse, 2nd Ed several times in the '90s and then gave away to David Gray (who didn't want it) I assume it is somewhere in the world of SIL-UK. C. Westfall and I used to talk about people like Longacre when she was working on her dissertation.
another search worth trying: "main line" narrative niccacci
C. Stirling Bartholomew