If you were to walk into a bookstore or library with a section on the New Testament, and if you were to look for the books that discussed Luke, chances are you’d find a large number of volumes combining Luke and Acts under whatever topic. So “A Commentary on Luke-Acts,” “A Theology of Luke-Acts,” “The Spirit in Luke-Acts,” and so on. This is true also of NT Introductions, which often discuss Luke and Acts together. On one level this makes sense; Luke is the author of both books, the introduction to Acts calls it the second part of a two part work, and there are a myriad of linguistic, narrative, and theological points of continuity.
But on another level, the canonical one, it makes little sense. The fact is that John almost always comes at the end of the Fourfold Gospel corpus (see Metzger, The Canon of the NT, 296), and there are only three cases of Luke coming at the end, each of which are late (6th, 14th cents.) and regionally isolated.
Why don’t we follow the overwhelmingly dominate order of the NT in our interpretive practice when discussing Acts? While I would not go so far as to say we should start having “John-Acts” monographs, we ought to consider seriously the fact that Luke almost never comes immediately before Acts in any of our available lists, codices, or MSS. The arrangement of material matters in interpretation, even on a canonical level, and John splitting Luke and Acts ought to give NT readers pause in how the interpret the NT exegetically, narratively, and theologically.