Wrap div-tag around posts in page

What happen if you proceed with the following syntax?

<div id="container">
<?php if( have_posts() ) : while( have_posts() ) : the_post(); ?>
    <article id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
        <h2 class="entry-title"><?php the_title(); ?></h2>
        <div class="entry-content">
            <?php the_content(); ?>
        </div>
    </article > <!-- /#post-<?php the_post_ID(); ?> -->
<?php endwhile; endif; ?>
</div> <!-- /#container -->

The additional things added:

• post_class()
• HTML5 semantic tag <article>, and
• The Loop

And:

Never ever repeat same ID on a single view