Learn Spanish (Latin America): El trabajo nos agota, pero no estamos para descansar. - The work exhausts us, but we are not in the mood to rest.

In this context, estar para followed by an infinitive expresses your current mood, state, or capacity to do something. Because it is negated as no estamos para descansar, it translates to "we are not in the mood to rest" or "we are in no condition to rest."

How would the meaning change if we used por instead of para?

This is a common mix-up! Estar para plus an infinitive is about your mood or readiness. On the other hand, estar por plus an infinitive typically means you are just about to do something, or that you are in favor of doing it. If the sentence said no estamos por descansar, it would mean "we are not about to rest" or "we are not in favor of resting."

Can I use estar para with nouns instead of an infinitive verb like descansar?

Yes! You can use this structure with nouns to mean you are (or aren't) in the mood for a specific thing. A very common phrase is no estoy para bromas, which means "I am not in the mood for jokes."

Why is it nos agota rather than agota a nosotros?

The word nos is a direct object pronoun showing who is being exhausted by the work, and these pronouns must go directly before the conjugated verb (agota). You can add a nosotros at the end for extra emphasis, but you cannot remove the nos.