Remember that serve means "to provide service". What service does a journalist provide to his readers? A journalist is supposed to provide readers with an honest and objective account of what he his reporting. So in this context, I believe it would mean that the journalist should remember he must report the truth because that is what the readers want.

In this case, the word serve means the journalist has the responsibility to act in the best interest of his readers. Or more simply put, to be useful to, or help his readers. So if the journalist had two ways to write an article, it is his duty to write the article that better helps his readers.