[WordPress] Themes: Populate the 'Posts Page' with content from the Editor.

functions.php

<?php

/**
 * Pull content from Posts Page into home template.
 *
 * @param WP_Query $query WP Query.
 *
 * @return WP_Query
 */
function ti_load_home_content( $query ) {

	// Discard if not the main query.
	if ( ! $query->is_main_query() ) {
		return;
	}

	// Stop if this is inside the WP Admin area.
	if ( is_admin() ) {
		return;
	}

	// Stop if we are not on the home (post archive) page.
	if ( ! is_home() ) {
		return;
	}

	$query->set( 'post_type', 'page' );
	$query->set( 'p', get_option( 'page_for_posts' ) );

	return $query;

}

add_action(
	'pre_get_posts',
	'ti_load_home_content'
);