The official WordPress Theme Review guidelines are fairly strict in some cases, and for a good reason: those best practices, tips and rules ensure that the risk of having bad code pushed to the ever growing themes and plugins repository is kept to the minimum.
One of those rules dictates that direct file operations aren’t allowed, unless they’re performed through the Filesystem API. Due to this restriction, the use of an handy function such as
file_get_contents is prohibited, and its occurrences in a theme are promptly signaled by the Theme Check plugin.
For local reads, though, there’s a way to access a file’s contents without invoking
$content = implode( ‘’, file( $path_to_file );
which essentially accesses the file, reads its lines into an array, whose elements are then joined in a single string.