What does a journalist should write only what he holds in his heart to be true mean?

This quote suggests that a journalist should only write about what they genuinely believe to be accurate and truthful, rather than simply reporting information without considering its validity or potential consequences. It emphasises the importance of integrity, honesty, and ethical behaviour in journalism, where the primary goal should be to inform the public with credible information, even if it may be unpopular or inconvenient to certain parties.