Pandas don’t have just one religion, but probably their most popular religion is this:
There are many gods. The goal of all the gods, except for maybe a few twisted ones, is to create the most perfect object possible in our universe. In fact, this is the sole reason our universe was created; any object created in the palaces of the gods, which lie beyond, is perfect by definition. The universe we live in was fabricated as a testing ground of sorts.
It is self-evident that the perfect object is a stalk of bamboo. The gods compete, each in their own ways, to make the best bamboo that can be made.
Pandas are arbiters. One cannot properly determine the worth of a stalk of bamboo without a panda to pass judgement. This is why pandas exist; they were added to our world in order to help the gods decide if their bamboo efforts had reached fruition. Before there were pandas, the arguments between the gods had consequences not to be desired.
This is why pandas must eat bamboo. It is a holy duty. It is not, as some might think, laziness or gluttony. By eating bamboo, pandas hasten the day when the goal of all the gods will be reached; and all will celebrate.
Some might ask if this goal should be reached, since — if the purpose of the universe is to test bamboo — the universe will be purposeless once the perfect bamboo is accomplished. Purposelessness is another word for “disposable.” Pandas, however, are not inclined towards long-term thinking. They simply enjoy bamboo.
With thanks, as always, to S.