Including Custom Template on template_include Filter not working

I would suggest you copy page.php into your custom template, and then modify the code as required. At the very least, your template should look something like:

<?php get_header() ?>

<?php while ( have_posts() ) : the_post() ?>

    <article <?php post_class() ?>>
        <?php the_title( '<h1 class="entry-title">', '</h1>' ) ?>

        <div class="entry-content">
            <?php the_content() ?>
        </div>
    </article>


<?php endwhile ?>

<?php get_footer() ?>