Answer:
The reason behind capitalizing "Posterity" is because the text talks about the coordination of ideals and efforts to create an environment to guarantee all those are accomplished.
Step-by-step explanation:
The capitalization of posterity provides the required importance to the word after exposing all the writer's arguments, in this case, the main objective of the text is to communicate that the group of the one the writer is talking about looks for posterity. Therefore it is the main topic of the text. The rest are supporting ideas to demonstrate the group is doing everything in its power to achieve it.