Why "this()" is not working here

Why "this()" is not working here

Hi,

This works:

  2.  if( $('.messages.error').length ) {
  3.        $('.messages.error').focus();
  4.      }

But this doesn't:

  2.  if( $('.messages.error').length ) {
  3.        $(this).focus();
  4.      }

Why?