A surah is different from a chapter for linguistic reasons. The word surah comes from “the outer walls of a city.” If you can visualize: in the old days, they didn’t have borders and signs saying
“Welcome to such-and-such city.” Rather, there were outer walls that you had to go through; it was a security measure. Inside of the city, there are a bunch of things happening – commerce, residences, markets, etc – but it is all connected. That is kind of what is going on in a surah – there’s a lot going on, but it’s all connected somehow.
- Nouman Ali Khan [in his Bayyinah tafseer discussion on Surah Naba']