We weren't supposed to bring in any outside texts, because we didn't have any outside texts in common. Now think of reading Hegel in senior seminar. Someone invariably brought up Kant, Plato, etc. in discussing Hegel, because we all had that as common background. Furthermore, Hegel had that as background when he was writing. For a minute let us think of the Bible in the same way.
Genesis is first.
Revelation comes last. The writer had the rest of the Bible as background, and if we read the Bible in order, so do we. We should probably read it in that context. Now here's the complicated part. The text itself implies that this is the case.