I think that emacs's core idea is a small core (pun intended) of functionality written in a high-speed language (C in emacs's case), entirely orchestrated and glued together in a high-productivity dynamic language (elisp).

Emacs really isn't a scriptable editor: it's an editor written in a 'scripting' language atop a relatively small set of primitives which happen to be useful for editing. But it's also an email client written in that same language, and a version-control interface, and a web browser, and a news client, and a Tetris game, and and and …