Emacs takes a bit to start up unlike Vim. This means that when I want to edit a file quickly (like… say a note on this website), but I want to edit it where I’m comfortable. While I know Vim very well, my emacs config is finished and easy to me and my current Vim setup isn’t as nice.
To get an existing emacs to open files from the terminal you need to run
M-x server-start. For me this is done already in spacemacs. Then you can just run
emacsclient to launch whatever files you want like you did with vim.
$ emacsclient -n content/notes/launch-existing-emacs-from-terminal.md
Credit where credit is due: Unix & Linux StackExchange