He, a journalist, believed profoundly in the craft and mission of serving the public’s right to know the news.
What meaning we can take here in the above sentence?
The 'craft' that the sentence is alluding to is Journalism. The American Press Institute defines the purpose of journalism as being "to provide citizens with the information they need to make the best possible decisions about their lives, their communities, their societies, and their governments." The sentence describes the same misison in fewer words, viz. "the public's right to know the news."
So the sentence is speaking about someone who is a journalist. This person has a deep interest in journalism as a craft, i.e. he presumably thinks that the news stories he writes should be well-researched, well-written, and present the facts in as clear and honest a fashion as possible. He also has a deep interest in the mission of journalism (i.e. "the public's right to know the news."). So, he does not think that news stories should be subject to censorship that would withhold all of the facts from the public.