If you need to make WordPress comments visible on the index page (not just within a post), add this line wherever you want comments to show:
<?php $withcomments = true; comments_template();?>
You might need to disable comments elsewhere in the template, or they might show up twice, but that depends on the theme.
One commenter wrote in another language that this may not work…perhaps it depends on the theme, but this is what worked for me on another blog.