Get_template_part() problem with the_content()

The problem is that you are running a loop from secondary query in front-page.php and the loop from main in page-home.php. So, the post data in page-home.php won’t be the data from the WP_Query in front-page.php.

Additionally, you are trygin to get full template files as template parts, which is not correct. I mean, front-page.php is a full template will header, content and footer and page-fome.php is also a full template with header, content and footer. You should re-think the logic to split template parts.

A basic (and silly) example to show you a correct approach:

front-page.php:

<?php get_header(); ?>

<?php 

    $query = new WP_Query('pagename=home');
    if ( $query->have_posts () ) : while ( $query->have_posts() ) : $query->the_post();

            get_template_part("content");

        endwhile; endif;
        wp_reset_postdata();

 ?>

<?php get_footer(); ?>

page-home.php:

<?php
/*
Template Name: Home
*/
?>

<?php get_header(); ?>
        <section id="first_section">
        <img class="jumbo wow bounceInDown animated" data-wow-delay="2s" src="https://wordpress.stackexchange.com/questions/197061/<?php echo get_template_directory_uri(); ?>/images/jumbo-illustration.png" alt="Webdesigner and Developer" />
        <div class="tagline-wrapper wow bounceInLeft animated" data-wow-delay="2.5s">

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

        get_template_part("content");

    <?php endwhile; ?>
    </div>
    <?php   else : ?>
        <p><?php _e( 'Sorry, no posts matched your criteria.' ); ?></p>
    <?php endif; ?> 


    </section>


<?php get_footer(); ?>

content.php:

<h3 class="tagline"><?php the_content(); ?></h3>