To make a concrete response to the appeal of our brothers and sisters in humanity, we must come to grips with the first of these challenges: solidarity among generations, solidarity between countries and entire continents, so that all human beings may share more equitably in the riches of our planet. This is one of the essential services that people of good will must render to humanity. The earth, in fact, can produce enough to nourish all its inhabitants, on the condition that the rich countries do not keep for themselves what belongs to all.