Displaying the post after entered - php

Question

I have some HTML and PHP code, which is responsible for basically, when some text is entered into a field, it should display as a post (which I have already made partially), and I have written the PHP code responsible for database insertion as well. However, the only thing I want to do is, when the user types in the field and clicks post, the post should display. So for that I tried some code, however it isn't working. When filled in and the post button is clicked, the post isn't displaying. What to do? Code:
PHP:
<?php
session_start();
// Making Connection To The Database
$dbHost = "localhost";
$dbUser = "root";
$dbPass = "";
$database = "signup";
$connection = mysqli_connect($dbHost, $dbUser, $dbPass, $database) or die ("Sorry, we could not connect to the database");
// Posting System
if (!empty($_POST['postContent'])) {
$post = $_POST['postContent'];
$firstname = $_SESSION['firstname'];
$lastname = $_SESSION['lastname'];
$sql = "INSERT INTO posts (firstname, lastname, body, date_posted) VALUES (?, ?, ?, NOW())";
$stmt = mysqli_stmt_init($connection);
// nested if statement
if (!mysqli_stmt_prepare($stmt, $sql)) {
echo "";
} else {
mysqli_stmt_bind_param($stmt, "sss", $firstname, $lastname, $post);
mysqli_stmt_execute($stmt);
}
} else {
echo "";
}
?>
HTML & PHP:
<style>
.postPFP {
margin-left: 680px;
width: 70px;
position: fixed;
margin-top: 20px;
cursor: pointer;
}
.info {
margin-left: 756px;
position: fixed;
font-family: 'Rajdhani';
font-weight: bolder;
margin-top: 25px;
}
.postOptions {
position: fixed;
width: 70px;
margin-left: 1176px;
margin-top: 16px;
}
.thepost {
margin-top: 55px;
position: fixed;
display: none;
}
</style>
<div class="thepost">
<?php
$sql = "SELECT * FROM posts";
$result = mysqli_query($connection, $sql);
if (mysqli_num_rows($result) > 0) {
while ($row = mysqli_fetch_assoc($result)) {
?>
<div class="postFormat">
<img src="img/pfp.png" alt="pfp" onclick="location.href='profile.php'" class="postPFP">
<b><div class="info"><?php echo $firstname . " " . $lastname ?></div></b>
<img src="img/options.png" alt="postOptions" class="postOptions">
<hr style="margin-top: 85px; width: 600px; position: fixed; margin-left: 663px; border:1px solid black; border-radius: 10px">
<hr style="margin-top: 85px; width: 0px; height: 215px; position: fixed; margin-left: 1150px; border: 1px solid black; border-radius: 10px">
<hr style="margin-top: 300px; width: 600px; position: fixed; margin-left: 663px; border:1px solid black; border-radius: 10px">
<p style="margin-left: 670px; margin-top: 95px; position: fixed; font-family: 'Rajdhani'"><?php echo $row["body"]; ?></p>
</div>
<?php
}
}
?>
</div>