Why is my Laravel 'show' controller not passing along the variable?

I currently have

GET|HEAD      forum/{forum}       App\Http\Controllers\ForumController@show

and

Route::resource('/forum', 'ThreadController');

and

public function show(Thread $thread)
    {
      return $thread;
    }

but when I go to 'forum/152' (post #152 in MySQL database) for example, the page only displays a blank '[]' array. How can I fix this so that the selected item shows? Thank you. :)

via Simon Suh