How to use a class within a cron job function

You’re calling a function with variables that are not defined and are required for the function to work correctly.

function hourly_function() {

   $newClass = new newClass();

   $var1 = 'this should';
   $var2 = 'work with';
   $var3 = 'some content';

   $newClass->newClass_function($var1, $var2, $var3); 
}

You might want to move those variable to a __construct

if ( ! class_exists('AClass')) {
    class AClass {
        function __construct( $var1 = null, $var2 = null, $var3 = null ) {
            //...
        }
    }
}
$instance = new AClass(1,2,3);

Or the __invoke method:

if ( ! class_exists('BClass')) {
    class BClass {
        function __invoke( $var1 = null, $var2 = null, $var3 = null ) {
            //...
        }
    }
}
$instance = new BClass();
$instance(1,2,3);