Create a reusable WordPress module with OOP.

class-example-module.php

<?php
/**
 * Class: Example Module
 *
 * @package projectname
 * @subpackage modules
 */

/**
 * Example Module
 */
class Example_Module {

	/**
	 * Construct
	 *
	 * @param bool|string $style_uri (Optional) Specify stylesheet URI.
	 */
	public function __construct( $style_uri = false ) {
		$this->styles( $style_uri );
	}

	/**
	 * Hero
	 *
	 * @param array $args Arguments.
	 */
	public function hero( $args = array() ) {
		$defaults = array(
			'heading' => 'Et eaque et suscipit et voluptate.',
			'content' => 'Placeat sunt deleniti. Sed eum aut neque laboriosam repellendus quaerat.',
		);

		$args = wp_parse_args( $args, $defaults );

		ob_start();
		?>
		<div class="hero">
			<h1 class="hero__heading"><?php echo esc_html( $args['heading'] ); ?></h1>
			<div class="hero__content">
				<?php echo wp_kses_post( $args['content'] ); ?>
			</div>
		</div>
		<?php
		echo wp_kses_post( ob_get_clean() );
	}

	/**
	 * Styles
	 *
	 * @param bool|string $style_uri External stylesheet.
	 */
	private function styles( $style_uri = false ) {
		ob_start();
		?>
		<style>
		.hero {
			background: #ddd;
			padding: 2em 6em;
		}

		.hero__heading {
			font-size: 2em;
		}

		.hero__content {
			max-width: 600px;
		}
		</style>
		<?php
		wp_register_style( 'case-study', $style_uri, array(), '1.0.0' );
		wp_enqueue_style( 'case-study' );
		wp_add_inline_style( 'case-study', ob_get_clean() );
	}
}

template-example.php

<?php
/**
 * Template Name: Example
 *
 * @package projectname
 * @subpackage templates
 */

get_header();

require_once module( 'class-example-module' );
$example_module = new Example_Module();

$args = array(
	'heading' => 'Some Custom Heading',
	'content' => 'Lorem ipsum dolor sit amet consectetur adipisicing elit. Suscipit corporis aliquam rerum eos ducimus error, repellendus ea velit unde ipsum cum delectus, quo magnam ut asperiores iure eius cupiditate nesciunt?',
);
$example_module->hero( $args );

get_footer();