instantiating variables

Hi,

i have a problem with instantiating variables

when i use this code in a taxonomy file, then everything works:

if ($term->name == "Rotwein") {
        if (have_posts()) : while (have_posts()) : the_post();
            echo $this->render('_post'); ?>
            <?php echo $this->render("_pagination", array("type" => "posts")); ?>
            <?php endwhile; ?>
            <?php else : ?>
            <h1 class="title"><?php printf(__("Sorry, but there aren't any posts in the %s category yet.", "warp"), '<span>' . $term->name . '</span>'); ?></h1>
           <?php get_search_form(); ?>
            <?php endif;
; ?>

now i want define the if/while (have_posts()) loop in a function…this function is in a mu-plugins folder in wp-content
but now i have the problem with $this->render…$this is not instantiated in order to use it in taxonomy file

so my question:
how can i make the code useable in my taxonomy file…?

something like this
wp-content/mu-plugins/wines.php:

function funcRedwine()
{
    if (have_posts()) : while (have_posts()) : the_post();
        echo $this->render('_post');
        echo $this->render("_pagination", array("type" => "posts"));
    endwhile;
    else : ?>
    <h1 class="title"><?php printf(__("Sorry, but there aren't any posts in the %s category yet.", "warp"), '<span>' . $term->name . '</span>'); ?></h1>
    <?php get_search_form();
    endif;
}
add_filter('content', 'funcRedwine');
?>

taxonomy-wines.php:

if ($term->name == "Redwine") {
      funcRedwine();
    } elseif ($term->name == "Whitewine") {
      funcWhitewine();
    }

any help would be appreciated

cheers
slotty