Service to mankind is beneficial if performed without egoism and doership. Otherwise, service with egoistic desire can be an obstruction for moksha, final liberation.To know more visit :

In English: https://www.dadabhagwan.org/path-to-happiness/humanity/help-others-the-purpose-of-life/what-is-service-to-self/

In Hindi: https://hindi.dadabhagwan.org/path-to-happiness/humanity/help-others-the-purpose-of-life/what-is-service-to-self/

In Gujarati: https://www.dadabhagwan.in/path-to-happiness/humanity/help-others-the-purpose-of-life/what-is-service-to-self/