Recent posts on homepage

First, ensure that your template file is named home.php.

Second, there’s no need to use a custom query loop in this context. If you only want to display 3 posts on the blog posts index (i.e. the “homepage”), then filter the main loop query via pre_get_posts:

function wpse83660_filter_pre_get_posts( $query ) {
    if ( is_home() && $query->is_main_query() ) {
        $query->set( 'posts_per_page', '3' );
    }
}
add_action( 'pre_get_posts', 'wpse83660_filter_pre_get_posts' );

And you can replace your entire recentPosts() function with a normal loop.

Thurd, you’re calling the_content() both outside of a loop instantiation, and expecting it to return content other than what it will return:

<?php get_header(); ?>
<?php the_content(); ?>
<?php get_footer(); ?>

This call to get_content() has 2 problems:

1. You haven’t instantiated a loop:

   if ( have_posts() ) : while ( have_posts() ) : the_post();
   

2. In the blog posts index context, this call to the_content() will return the content of the posts in the blog posts index, not the content of the *page assigned as page_for_posts

By solving the second problem, we’ll fix the first as well.

To get at the post_content for the page assigned as page_for_posts, use get_page(), and pass it get_option( 'page_for_posts' ):

$page_object = get_page( get_option( 'page_for_posts' ) );

Then, output its results:

if ( ! is_null( $page_object ) ) {
    echo apply_filters( 'the_content', $page_object->post_content );
}

So, your entire template file will look like so:

/**
 * Blog posts index template file
 *
 * Displays the blog posts index
 * 
 * @filename: home.php
 */

get_header();

if ( have_posts() ) : while ( have_posts() ) : the_post();

    <a href="https://wordpress.stackexchange.com/questions/83660/<?php the_permalink();?>"><?php the_post_thumbnail('recent-thumbnails'); ?></a>
    <h2><a href="<?php the_permalink(); ?>"><?php the_title();?></a></h2>
    <?php the_content(); ?>

endwhile; endif;

$page_object = get_page( get_option( 'page_for_posts' ) );
if ( ! is_null( $page_object ) ) {
    echo apply_filters( 'the_content', $page_object->post_content );
}

get_footer();