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.
Thanks to Spacemacs, Emacs is already better Vim than Vim itself. I know what I'm talking about. I'm a die-hard vimmer.