$file "is" the file resource; you don't want to print that but rather the return value of fread(), i.e. the contents of the file.
But then again you don't want to send the "raw" contents of the file, as it might (and probably will) contain something that will break your html structure.
At the very least you should use htmlspecialchars()
<?php
$filePath = $_GET["field2_name"];
// you really should add more security checks here
// just imagine a request like field2_name=../../../etc/something.txt
$url = "cs_data/home/" . $filePath;
$contents = file_get_contents($url);
echo '<div class="comment">', htmlspecialchars($contents), '</div>
You might also be interested in highlight_file():
<?php
$filePath = $_GET["field2_name"];
// you really should add more security checks here
// just imagine a request like field2_name=../../../etc/something.txt
$url = "cs_data/home/" . $filePath;
echo '<div class="comment">';
highlight_file($url, false);
echo '</div>';