类PHP中的奇怪错误对象

I have a strange problem, can not enter in class with $_POST, very strange, here is the problem and error? Class is simple just for demonstration.

if(isset($_POST['name']))
{
$name=$_POST['name'];
$email=$_POST['email'];
$comment=$_POST['comment'];
$komentar = new comments($name,$email,$comment);
$komentar->provera();
}

Class:

class comments 
{
public function __construct($name, $email, $comment)
{
$this->name=$name;
$this->email=$email;
$this->comment=$comment;
}
public static function provera()
{
$poruka=$this->comment; 
echo $poruka;
}
}

I got this error

Fatal error: Using $this when not in object context in 
classes\comments.inc.php on line 12

You can't use $this in a static method. Unless you need provera() to be called statically, remove the static keyword from its declaration.