PHP: scope of global keyword

My_Page_Template.php

<?php
/**
 * Template Name: My Page Template
 */
?>
<?php // the_post() already uses `global $post;`, so why is it needed again on line 11 in content-my_page.php? ?>
<?php while (have_posts()) : the_post(); ?>
  <?php get_template_part('templates/page', 'header'); ?>
  <?php get_template_part('templates/content', 'my_page'); ?>
<?php endwhile; ?>

content-my_page.php

<div class="row">
  <div class="content-main">
    <?php

    // check if the flexible content field has rows of data
    if( have_rows('flexible_blocks') ):
         // loop through the rows of data
        while ( have_rows('flexible_blocks') ) : $row = the_row();
            switch (get_row_layout()) {
              case 'inserted_content':
                global $post; // <-- Why is this required in order the following call to post_class() to work?
                $post = get_post( get_sub_field('inserted_item') );
                setup_postdata( $post );
                ?>
                <article <?php post_class(); ?>>
                  <div class="aggregate-main">
                    <?php  vpa_render_post_object( $post ); ?>
                  </div>
                  <?php if ( embedded_has_supplemental($row) ) : ?>
                  <aside class="sidebar">
                    <?php acf_the_supplemental( $post->ID ); ?>
                  </aside>
                  <?php endif; ?>
                </article>
                <?php
                break;

              default:
                # code...
                break;
            }
        endwhile;
            reset_rows();

    else :

        // no layouts found

    endif;

    ?>

  </div>
</div> <!-- .row -->