see my comments in your code
<?php
// set the post ID that you want to use and use it in all
// of the function calls where it is needed
// and make sure it's an integer value
$post_id = intval(get_option('page_for_posts'));
// thjis is a repeater or flex field according to the code below
// useing the_field() will output an array because a repater
// returns an array if you do not use a have_rows() loop
the_field('blog_introduction', get_option('page_for_posts'));
?>
<div id="introParagraph" class=" col-xs-12 p-y-2">
<?php
if (have_rows('blog_introduction', $post_id)) {
while(have_rows('blog_introduction', $post_id)) {
the_row();
?>
<h1 class="text-xs-left col-xs-10 col-md-offset-1 m-b-1">
<?php
the_sub_field('page_header'); ?>
</h1>
<div class="col-md-3 col-md-offset-1 col-xs-7 m-t-1">
<h3 class="text-xs-left" id="headerDescription">
<?php
the_sub_field('page_description_paragraph');
?>
</h3>
<?php
} // end while
} // end if
?>
</div>
