The ASP engine reads line-by-line. If it encounters a call to a function or an object that is in an include file before it includes the file, then it won't be able to find the object or function. Ex:
<!--#include "whatever.asp"-->
set something = new somethingorother
This will work when somethingorother is defined in whatever.asp. However, this:
set something = new somethingorother
<!--#include "whatever.asp"-->
will not work because you're trying to create a new something of type somethingorother, but somethingorother hasn't been defined because the file hasn't been included yet.