To use emacs as a server, look into gnuserv. From the manpage:

       gnuclient  allows the user to request a running emacs pro-
       cess to edit the named files or directories and/or  evalu-
       ate  lisp forms.     Depending on your environment, it can be
       an X frame or a TTY frame.  One typical use  for     this  is
       with  a    dialup    connection to a machine on which an emacs
       process is currently running.

      gnuserv is the server program that is set running by emacs
       to  handle  all    incoming and outgoing requests. It is not
       usually invoked directly, but is     started  from    emacs  by
       loading    the  gnuserv package and evaluating the Lisp form
       (gnuserv-start).
[download]

Using gnuserv and gnuclient also addresses Aristotle's concern about the heavy startup costs of invoking emacs for each separate command.