What does planetary common good mean?

it provides good for the common if your smart!

The commitment to promote the general welfare of all persons, as opposed to protecting the interests of a narrow section or class of the population, encapsulates what is most unique about the United...

I would say it means that rather than thinking of what would benefit them the most they decided what would benefit the group the most.

Try and learn, develop an understanding for people, and try to see their best. Just watch, untill you understand what's going on.