The V-Shaped Gospel

For the last six years my eyes and ears have been attuned to a spatial reading of the Scriptures. I wrote my first book on the spatial nature of the kingdom and have plans at some point to write a biblical theology of the descent-ascent theme that is found across the canon of Scripture. Recently I picked up Matthew Bates newest book, “Salvation by Allegiance Alone.” In the first part of the book, he gives an argument for what I would call a “wide angle lens” of the gospel, but he employed imagery that resonated with me. He argues that the gospel has a V-shape (he admits he heard this from Ben Witherington first). What does he mean by this?