Why is writing about a great politician considered a lesser form of service than writing about a saint?

As detailed in Chapter 0, the service of writing a biography for a worldly Guru, such as a politician or jurist, is of a worldly nature. While it may serve the public and have educational value, its importance and fruit are not eternal because this service is limited by space and time. The text states that it is also rooted in self-interest and therefore does not yield spiritual fruits. In contrast, writing about saints is a form of Guru service that does yield spiritual fruits, making it a spiritually superior, though still potentially partial, form of service.