// Show posts in order of post__in array
$id_array = array(589,39,981,531);
$args = array(
   'post__in' => $id_array,
   'ignore_sticky_posts' => 1,  // Stickies will mess this up
);
query_posts($args);
if (have_posts()) :
   usort($wp_query->posts, function($a, $b) use ($id_array) {
      return array_search($a->ID, $id_array) - array_search($b->ID, $id_array);
   });
   while (have_posts()) :
      // Put your own loop code here
      the_post();
      echo "<p>ID: $post->ID</p>";
   endwhile;
endif;