If you’ve built your WordPress theme to use the Featured Image functionality, your RSS feed subscribers are missing part of your post.
When you use a small thumbnail, you may not think much about it. However, there may be instances where you want to include your post thumbnail. Of course, there are those WordPress theme designs that include a large wide Featured Image that can add a lot to the feeling of a post. Sure, you could simply insert the image at the top of the post, but there are some other functions you can do in WordPress by calling a posts Featured Image.
With this WordPress snippet, you can have the best of both worlds. Here’s how to add your post thumbnail/Featured Image to your RSS feed:
How-To Add Post Thumbnails to Your RSS Feed
As with many WordPress snippets, you’ll be dropping this into your theme’s functions.php or wrapping it up with your own functionality plugin.
$content = '<p>' . get_the_post_thumbnail($post->ID) .
'</p>' . get_the_content();
As long as your theme supports post thumbnails, you should be good to go!