If you want to add a message or comment note that will be visible to all users who are leaving a comment on your WordPress site, you can try the code below :
function ogbongeblog_comment_text($arg) {
$arg['comment_notes_before'] = "We're glad you have chosen to leave a comment. Please keep in mind that comments are moderated according to our <a href='https://www.ogbongeblog.com/comment-policy'>comment policy</a>. Your email address is required but will not be published. No keyword stuffing in the name field and commenting from blah blah blah makes no sense";
return $arg;
}
add_filter('comment_form_defaults', 'ogbongeblog_comment_text');
Add the code in your theme’s functions.php file.
The code will simply replace the default comment form before notes.
Remember to change the URL accordingly, so it goes to your comment policy page rather than ogbongeblog.com 
You can steal our comment policy page though and modify it to meet your needs. 
Enjoy!
