What is the purpose of a public service advertisement?
to convince people to take action on an important topic
to persuade people to buy a new product
to notify people of upcoming social events in their community
to educate people about past historical events

The answer is to convince people to take action on an important topic

the anwser is went creeping down the river again, across the wide lonely marshes to the sea.

i longed to go with them out into the world to seek my fortune in foreign lands—africa, india, china and peru!

and, dreaming of the lands i had never seen, i'd sit on there, watching till they were out of sight.