Change the_content() in Theme Thirteen

by

You probably have a read more tag in your posts, so you will need to remove them.

We can use the the_content filter to achieve that. We need to search and replace the <!--more--> tag with nothing.

You can try the following: (NOTE: The following code is untested)

add_filter( 'the_content', function ( $content )
{
    return str_replace( '<!--more-->', '', $content );
}, 11 );