That’s because you can’t pass the post ID to the
the_content() function. Please check this page to learn more about it: https://codex.wordpress.org/Function_Reference/get_the_content.
If you want to get the content, you need to use the
get_post() function instead. This page should give you more idea about it: http://wordpress.stackexchange.com/questions/9667/get-wordpress-post-content-by-post-id.
I hope this helps 🙂