"I gave my word that this source would not be identified unless he changed his mind. He has not"

Bob Woodward is indicating that he has actually made a pledge to a source that their identity would remain anonymous unless the source changed their mind. This implies that the source has a specific level of trust in Woodward, as they want to supply information without the fear of being recognized. Woodward is also suggesting that the source has actually not altered their mind, which they are still happy to remain confidential. This could be translated as a sign of regard from Woodward to the source, as he is honoring their desires to stay confidential. Woodward is likewise indicating that he is a credible source, as he is willing to keep his word and not expose the source's identity. This quote is a testimony to Woodward's dedication to protecting the identity of his sources, and his dedication to maintaining his pledges.