In this example, we're checking if the user is authenticated (i.e., if their user ID is stored in the session). If they're not authenticated, we store a warning message using PHP Message show and redirect them to the login page. When they log in and are redirected back to this page, the message will be displayed using the PHP Message show library. PHP Message show is not a specific package or library, but rather a general concept for displaying messages to users in PHP web applications. There are many different packages and libraries that provide this functionality, such as Laravel's Flash package or the PHP-Alert library.