How can characters advance the plot

Read the excerpt from it's our world, too! : young people who are making a difference. the author’s purpose in this excerpt is to

Before ending this lesson, take a moment to review an informative research essay you have written. you’ve probably already written a conclusion to the essay. but is it the best conclusion it can be? does it properly summarize the main subtopics of your essay? does it state in one or two sentences the “so what” of your topic. if your topic was abraham lincoln, your essay shouldn’t be just about abraham lincoln. it should answer, “so what about abraham lincoln? ” take five or ten minutes, and looking only at that single paragraph, revise your conclusion

Why does the host answer the guest with brief responses during the party?