Easy reading or transfer of data from posts?

do_shortcode([espro-slider id=21]) will process the shortcode and return the result. The Codex describes exactly this example:

// Use shortcode in a PHP file (outside the post editor).
echo do_shortcode( '' );

You can often just call the callback directly also:

function generic_shortcode_callback($atts,$content) {
  return "Yay! ".$content;
}
echo generic_shortcode_callback('',' Me!');

VS:

function generic_shortcode_callback($atts,$content) {
  return "Yay! ".$content;
}
add_shortcode('yay','generic_shortcode_callback');
$sc = do_shortcode('[yay]Me[/yay]');
echo $sc;