functions within function?

Saw this example on the web. What's the purpose of the two functions being contained in a function? Why would someone put that top line in there? The two functions should work without it I would think.

Code:

$(function () {
  $("div.class").click(function(){
    //Doo something

  });

  $("div.secondclass").click(function(){
    //Doo something
  });

});