This clause is usually used together with the next sentence in the original poem:

> 先天下之忧而忧，后天下之乐而乐

> (put the world's worries before yours, and put your happiness after the world's) > edit: this translation is wrong, and raincole has a definitely better translation

Since the model is a language model, they probably use this to demonstrate the model's language capabilities – the model should be able to complete the whole sentence pair. The paper also mentions this:

> To ensure the model’s language capabilities, we introduced 10% of in-house text-only pretrain data.

So I believe it is just a text-only demonstration.