Is there some reason Lisp is superior to any other general-purpose programming language for text editing? I'm skeptical because to my knowledge, Emacs is the only major text editor written in Lisp.
purely for text editing? No. But that's not what distinguishes Emacs, it's famously very mediocre at it. The point of Emacs is to be a fully transparent, inspectable, dynamic and changeable environment. In spirit similar to Smalltalk systems like Pharo. And for that a Lisp is not the only choice but a very good one.
There's very few languages and environments that facilitate jumping into any place, making a change, compiling or evaluating a block of code or treating it as data and continuing seamlessly.
I disagree. Every time I use another editor I lament missing features when it comes to editing text. Like most editors (vim excluded) have pretty lackluster undo, transpose, case altering, and text reflowing commands.
You can think of Emacs as a kind of software Lisp machine with an emphasis on editing. Although that analogy only works well if you squint or if you don't know a lot about Lisp machines.
As someone who first learned Lisp through Emacs Lisp, I found it fun, well-documented, and powerful. Once you grok the basics of how the system is dynamically glued together, infinitely hackable, and self-documenting it's kind of mind-blowing.
Still, the reason for choosing a language for whatever are always more social and path-dependent than technical (reason 1: initial developer of whatever really likes the language, reason 2: language is seen as hip within some crowd, reason 3 (later in the game): management feels language is safe). Technical reasons for choosing a language typically tend to be post-hoc rationalizations. (I mean, no sane person would choose Javascript for an editor based on technical reasons alone, yet here we are.)
[0] https://lem-project.github.io/ [1] https://www.lispworks.com/products/lispworks.html
CL is also held together - and held back, hugely - by the standard that won't ever be updated. It's good to have it, but there are major omissions (code walkers, MOP) that won't ever be fixed.
As it is now, Elisp is more practical as a scripting language than CL. The gap will only continue to grow. Right now, CL has an edge in parallelism - native threads and mutexes (with all the problems they entail) work there, while with Emacs, the only parallelism you can get is through separate processes. On the other hand, async/await-style concurrency works quite well in Emacs, while in CL you're basically a few macros away from raw promises, and the only real asynchrony is through a pool of threads executing callbacks, and it doesn't play well with conditions and restarts and some other advanced features (notably absent from Elisp).
I love CL, but right now it's aged considerably, lost many of its unique advantages, and has little chance of ever catching up. It's a shame, but using CL in 2026 is not a superpower anymore - it's just one of the similarly-valued propositions, competing with other dynamic languages, still providing a few unique advantages, but even those are being implemented in other languages fast.
BTW emacs is written in C.
Even if you interpret emacs strictly as an interpreter of elisp, that interpreter is written in C, not elisp.
If you removed all elisp from the emacs distribution, you would still have an extensible windowed text editor. And you could add any desired functionality by writing elisp. Take C code away and you've got nothing functional.