When you configure your blog (posts) page under Settings > Reading, that page becomes nothing more than a placeholder – in other words, you won’t be able to grab it’s title/content within index.php
without a little trickery:
if ( $page_id = get_option( 'page_for_posts' ) ) {
echo get_the_title( $page_id );
// the_content() doesn't accept a post ID parameter
if ( $post = get_post( $page_id ) ) {
setup_postdata( $post ); // "posts" page is now current post for most template tags
the_content();
wp_reset_postdata(); // So everything below functions as normal
}
}