the codes listed here is part of the following article : https://www.mwordpress.net/how-to-add-read-more-for-wordpress-post-in-home-page/

read-more-functions.php

/*
 * get content and clean
*/
function mwp_post_content($post_id) {
	$post 		= get_post($post_id);
	$output 	= $post->post_content;
	$replace 	= "@(https?://([-\w\.]+[-\w])+(:\d+)?(/([\w/_\.#-]*(\?\S+)?[^\.\s])?)?)@";
	$output 	= wp_strip_all_tags($output, true);
	$output		= strip_shortcodes($output);
	$output 	= ltrim($output);
	$output 	= trim($output);
	$output 	= preg_replace($replace, '', $output);
	return $output;
}
/*
 * Content Word Limit
*/
function content($limit, $post_id) {
	$data 		= mwp_post_content($post_id);
	$content 	= explode(' ', $data, $limit);
	if (count($content) >= $limit) {
	array_pop($content);
	$content = implode(" ",$content).'…';
	} else {
	$content = implode(" ",$content);
	}
	return $content;
}

read-more-limit-example.html

<div class="textPreview">
<?php echo content(30, $post->ID); ?>
</div>

read-more-the-content.html

<div class="textPreview">
<?php the_content('More …'); ?>
</div>

read-more-the-excerpt.html

<div class="textPreview">
<?php the_excerpt(); ?>
</div>