为什么我可以下载用htaccess文件保护的文件？

This is the htaccess file:

ErrorDocument 400 /index.php
   ErrorDocument 401 /index.php
   ErrorDocument 403 /index.php
   ErrorDocument 404 /index.php
   ErrorDocument 405 /index.php

   <Files configure.php>
      order allow,deny
      deny from all
   </Files>

the file configure.php is in some folder lets say /config/configure.php and now the problem is that I can download it ! by just making a link to it. And it is because of this line ErrorDocument 404 /index.php, when I delete this line I get a 404 error and cannot download the configure.php file. But why is it like so that this line (that I want to have) makes it possible to download the configure.php file ?

You need to place the .htaccess file (not htaccess without the leading dot) into the folder where configure.php resides in (at least) to make the <Files configure.php>-directive^Docs work. See as well Filesystem, Webspace, and Boolean Expressions^Docs.