index.php

<?php
/**
 * The main template file
 *
 * This is the most generic template file in a WordPress theme
 * and one of the two required files for a theme (the other being style.css).
 * It is used to display a page when nothing more specific matches a query.
 * E.g., it puts together the home page when no home.php file exists.
 *
 * @link https://developer.wordpress.org/themes/basics/template-hierarchy/
 */

use Timber\Timber;

$templates = [ 'templates/index.twig' ];

if ( is_home() ) {
	array_unshift( $templates, 'templates/front-page.twig', 'templates/home.twig' );
}

$context = Timber::context(
	[
		'foo' => 'bar',
	]
);

Timber::render( $templates, $context );