Model Checkout Order confirm vs update

[gaashby]

Can anyone tell me

1) the difference between the "confirm" and the "update" methods
if (!$order_info['order_status_id']) {
$this->model_checkout_order->confirm($order_id, $order_status_id, $message);
} else {
$this->model_checkout_order->update($order_id, $order_status_id, $message);
}

2) why a payment process would follow the above with
$this->model_checkout_order->confirm($order_id, $this->config->get('config_order_status_id'), $message);

3) Why the content of my $message variable does not make it to the Order comment section.

thanks