Variables scope

I am using one of the pages, to display a list. I have the following in the page:

<? php
include_once "myFunctions.php";
include_once "myDeclarations.php";
displayText();
?>

Inside myFunctions.php, I have the following function:

function displayText() {
GLOBAL $textToDisplay;
echo "Testing WordPress";
echo $textToDisplay;
}

Inside myDeclarations.php, I have the following:

$textToDisplay = “This is a test”;

When I go to that page, it only displays: Testing WordPress. The variable $textToDisplay is not passed. It seems as if the include file that has the function in it, is recognized, but the variable in the other file, is not. How do I deal with this scope issue in WordPress?