Reddit mentions of The Church: The Gospel Made Visible (9Marks)

In addition to all the great suggestions already in this thread, I'll recommend two more specific, narrowly-focused books by Mark Dever: The Church and By Whose Authority? Elders in Baptist Life. I know that you're not looking for full-length books right now, but both of these are fairly short, easy reads.

One of the biggest points of divergence between Reformed Baptist theology and pretty much all other branches of Reformed theology is the issue of ecclesiology. Whereas most other branches of Reformed theology place a great emphasis on structure, authority, and upward chains of accountability within denominations, a central tenant of Baptist theology has always been local church autonomy. Thus, because each church is in charge of its own structure and is beholden only to itself, it's hard to make blanket statements about Reformed Baptist ecclesiology. That being said, I think Mark Dever's two books do a great job of explaining some good, solid principles from a distinctly Reformed Baptist perspective. Often, a lot of Baptist churches with a reformed bent merely accept a Calvinist soteriology without really incorporating too much more from Reformed traditions. Dever, on the other hand, really focuses a lot on the structure, function, and purpose of the church in his writings in a way you don't see that often, especially from big name, prominent Baptists.