how to add fields from referenced node drupal 8

I have a content type that contains a field that is a reference to another node. I'm trying to include a field from the referenced node within the page for the main node, but I can't figure out how to add that. Here's how I'm getting the value within my theme:

function mytheme_preprocess_node(array &$variables) {

  $node = $variables['node'];
      if ( $node->get('field_testimonial') ) {
          $referenced_nodes = $node->get('field_testimonial')->referencedEntities();
          if ( count($referenced_nodes) > 0 ){
            $referenced_node = $referenced_nodes[0];
            //this is providing the value I want.  how can I add that back to my page?
            error_log($referenced_node->body->value);
          }
      }
}

Please help me add that value back to my variables so I can use it in my theme! Thank you for your help.

Just do the following

$variables['referenced_body'] = $referenced_node->body->value;

In your Twig-Template you can do this:

{{ referenced_body }}