As of version 1.1.8 the theme is compatible with MailChimp for WordPress
When you create a form with the plugin add the following as the Form Code:
<input type="email" name="EMAIL" placeholder="Your email address" required /> <input type="submit" value="Sign up" />
That ensures correct styling and layout for the form with the theme.
Subscribe Form On Homepage
Head over to WP admin > Appearance > Customize > Subscribe > General. For the Shortcode option add the shortcode given by the plugin, it looks like [mc4wp_form id="531"]
Head over to WP admin > Appearance > Widgets. Add the widget called Meridian Theme - Subscribe to the desired location and in the Shortcode option add the shortcode given by the plugin.