Editing the default page to show all posts, rather than most recent ones

you have to set “post_per_page” to “-1”. Add this code to your home or index.php.

WP_Query (recommended)

$args = array('posts_per_page' => -1);
$the_query = new WP_Query( $args );

if ( $the_query->have_posts() ) {
  while ( $the_query->have_posts() ) : $the_query->the_post();
    the_title();
    the_content();
  endwhile;

  /* Restore original Post Data */
  wp_reset_postdata();

} else {
  // no posts found
}

query_posts() way

// Args that you pass to loop
$args = array('posts_per_page' => -1);

// The Query
query_posts( $args );

// The Loop
while ( have_posts() ) : the_post();
    the_title();
    the_content();
endwhile;

// Reset Query
wp_reset_query();

Alternatively you can go to Dashboard -> Settings -> Reading and set maximum posts per page to “1000” or something.