Since the eight characters are predestined, why should we worship Buddha and believe in Buddha?

There is a reason, and there will be results. So in Buddhism, everything is impermanent, there is no fixed life and destiny, everything is under your control, and you don't want to change it. No one can replace it.

The eight characters refer to the origin and fate, and worshipping Buddha and believing in Buddha is to change fate. Fate has a reason, and then it changes. Believing in Buddhism is a way to change yourself, not an end.