Show an Urgent Message in the WordPress Admin

Add the following code to your WordPress theme’s function.php file, or a functionality plugin

/**
 * Generic function to show a message to the user using WP's
 * standard CSS classes to make use of the already-defined
 * message colour scheme.
 *
 * @param $message The message you want to tell the user.
 * @param $errormsg If true, the message is an error, so use
 * the red message style. If false, the message is a status
  * message, so use the yellow information message style.
 */
function showMessage($message, $errormsg = false)
{
	if ($errormsg) {
		echo '<div id="message" class="error">';
	}
	else {
		echo '<div id="message" class="updated fade">';
	}

	echo "<p><strong>$message</strong></p></div>";
}