Display all posts from specific categories on a page

I want to display all posts from specific categories on a single page.
Therefore I edited the page.php file in my theme folder.
I added an ‘if-clause’ to check which page currently being displayed and load all posts from the following categories.

<?php get_header(); ?>

<div id="primary">
    <div id="content" role="main">

<?php
    if (is_page(26)) {
        query_posts('cat=2,6,9,13&showposts=-1&orderby=date');    
        if (have_posts()) : 
            while (have_posts()) : 
                the_post(); 
                get_template_part( 'content', 'page' );
            endwhile; 
        endif;  
    } else {
        while ( have_posts() ) : 
            the_post(); 
            get_template_part( 'content', 'page' ); 
        endwhile; // end of the loop. 
    }
?>

    </div><!-- #content -->
</div><!-- #primary -->

<?php get_footer(); ?>

But when I load my page 26 nothing will be displayed.

I’d Advise adding the arg of the category in an array. And don’t use query_posts.
Also showposts is deprecated use posts_per_page instead.

$args = array (
    'cat' => array(2,6,9,13),
    'posts_per_page' => -1, //showposts is deprecated
    'orderby' => 'date' //You can specify more filters to get the data 
);

$cat_posts = new WP_query($args);

if ($cat_posts->have_posts()) : while ($cat_posts->have_posts()) : $cat_posts->the_post();
        get_template_part( 'content', 'page' );
endwhile; endif;