Epistles are real correspondence
The New Testament letters have fit into my mental model as a synopsis of the whole Bible, and the Old Testament primarily as historical background. If the Bible were written as I imagine, the letters would be the treatise, and the Old Testament would be an appendix.
The claim that the letters are real correspondence rooted in the circumstances of the Roman Empire is scandalous. This means that the central content of the Bible is actually the Old Testament and the Gospel accounts, and the letters are nearer to practical footnotes on how to understand and apply the core than a synopsis of it.
Nowhere in the Bible exists a systematic theology or practical guide as I might expect. This surprises my cultural expectations and emphasizes the centrality of the complete narrative for all humans need, not just the final bits that we (mistakenly) assume are more relevant or applicable.
The nature of the epistles as actual letters opens the door for modern-day epistle-writing. Martin Luther King Jr’s birmingham epistle is a vivid example.
Aside
Thanks to Tim and John at The Bible Project for continuing to expand my imagination and challenge my assumptions about the Bible, and the Letter podcast series in particular.