Include content from one page to another

Another shortcode option (add the following to your functions.php). With this one, you have two options. You can query by the post/page ID (will work for any post type), or the page name/slug (only works for pages).

// Add "Show Content" Shortcode
function wpse_120886_show_content( $atts ) {
    // Attributes
    $a = shortcode_atts(
        array(
            'id' => null,
            'page_name' => null,
        ), $atts )
    );
    // Get Content & Return
    if ( $a['id'] ) {
        $the_post = get_post( $a['id'] );
        $the_content = $the_post->post_content;
    } elseif ( $a['page_name'] ) {
        $the_post = get_posts( array( 'name' => $a['page_name'], 'post_type' => 'page', 'post_status' => 'publish', 'posts_per_page' => 1 ) );
        $the_content = $the_post[0]->post_content;
    }
    return $the_content;
}
add_shortcode( 'show_content', 'wpse_120886_show_content' );

Usage:

By ID: [show_content id="ID_HERE"]

By Name/Slug: [show_content page_name="contact_text"]