Just crop the post body when we are in the posts page. Something like this:
<div class="post-body">
<?php if (is_postspage()): ?>
<?php echo create_summary(article_html()); ?>
<?php else: ?>
<?php echo article_html(); ?>
<?php endif; ?>
</div>
Then you need to add this function to crop the article body HTML. So that it will becomes the post snippet:
function create_summary($html) {
return '<p>' . substr(strip_tags($html), 0, 250) . '…</p>';
}