Being an Emacs enthusiast myself, it always surprises me how much more popular VIM is. Is this because VIM is taught more in schools? Maybe because VI/VIM is typically installed by default on Linux systems?
I hope you're not trying to explain the value and satisfaction of customization to an Emacs enthusiast!
The thing is an interpreter for Elisp, which the text editor is written and configured in. You can change the core functionality of the editor if you wanted, by writing some code in a buffer and pressing C-M-x. You can make it act exactly like vim if you wanted to. You can add line numbers on the side, better autocomplete for commands and searches, a git porcelain, new modes for different types of files. You can implement an IRC client, a browser, tetris, a file browser, or an email client; or you can just use the implementations that come included.
You can spend a lifetime configuring Emacs, and if you have attained the ultimate configuration, you'll look back at the end of your life and realize that it was worth the thousands of hours you put into it. But if you have not, don't worry: you'll be reborn into the cycle constant suffering-due-to-inferior-configuration until you figure it out.
The default modal keybindings are fantastic for editing text, once you start learning them it becomes addictive. Once you've learned most of them everything else feels annoyingly clunky.
I sometimes use IntelliJ and sublime but if I'm sshing around our network or editing random configs vim is the one that jumps to hand, and it's pretty much my default for everything now. Vim modes in those two IDEs are also pretty good.
EDIT: vimscript kind of sucks though, Emacs is way better on that front
The biggest game-changer for me in converting/sticking with emacs was finding out I can edit remote files with my local emacs via TRAMP (https://www.emacswiki.org/emacs/TrampMode). No more logging into remote machines and installing a sub-standard subset of my highly customized editor configuration.
And before you say it, yes I know you can edit remote files with vim too. But with emacs/TRAMP it's dead simple.
Also, the feeling that one's keyboard ought to have 'meta' and 'super' keys.