PHP表单与验证&；成功信息

我正在创建一个from，并使用PHP进行验证。我想隐藏表单，并在所有验证完成后显示成功消息。这是我正在使用的代码，你能告诉我为什么表单总是隐藏而成功消息没有显示吗：

      <?php
// defining variables and set to empty values
$nameErr = "";
$emailErr = "";
$numberErr = "";
$name = "";
$email = "";
$number = "";
$comment = "";
function test_input($data) {
  $data = trim($data);
  $data = stripslashes($data);
  $data = htmlspecialchars($data);
  return $data;
} 
if ($_SERVER["REQUEST_METHOD"] == "POST") {
  if (empty($_POST["name"])) {
    $nameErr = "Name is required";
  } else {
    $name = test_input($_POST["name"]);
    // check if name only contains letters and whitespace
    if (!preg_match("/^[a-zA-Z ]*$/",$name)) {
      $nameErr = "Only letters and white space allowed"; 
    }
  }
  if (empty($_POST["email"])) {
    $emailErr = "Email is required";
  } else {
    $email = test_input($_POST["email"]);
    // check if e-mail address is well-formed
    if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
      $emailErr = "Invalid email format"; 
    }
  }
  if (empty($_POST["number"])) {
    $numberErr = "Contact Number is required";
  } else {
    $number = test_input($_POST["number"]);
    // check if number only contains letters and whitespace
    if (!preg_match("/^[a-zA-Z ]*$/",$number)) {
      $numberErr = "Only letters and white space allowed"; 
    }
  }
  if (empty($_POST["comment"])) {
    $comment = "";
  } else {
    $comment = test_input($_POST["comment"]);
  }
  function form_submission_success(){
    echo 'Form submitted';
  }
  function submit_database(){
  }

  form_submission_success();
} else {
?>
        <p><span class="error">* required field.</span></p>
            <form method="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>">  
              Full Name: <input type="text" name="name" value="<?php echo $name;?>">
              <span class="error">* <?php echo $nameErr;?></span>
              <br><br>
              Contact E-mail: <input type="text" name="email" value="<?php echo $email;?>">
              <span class="error">* <?php echo $emailErr;?></span>
              <br><br>
              Contact Number: <input type="text" name="number" value="<?php echo $number;?>">
              <span class="error">* <?php echo $numberErr;?></span>
              <br><br>
              Comment: <textarea name="comment" rows="5" cols="40"><?php echo $comment;?></textarea>
              <br><br>
              <input type="submit" name="submit" value="Submit">  
          </form>
          <?php } ?>

按照同样的逻辑，我会将所有条目提交到数据库中，但一旦所有赋值完成。