© Sergej Gunjejev
In the Russian system the Chief of Staff and Head of the Executive Office has a key role coordinating the various departments of the government, acting as the transmitter to the bureaucracy of the President's orders. This is therefore a critical position at the very centre of the Russian power structure and the official who occupies it is by definition a most important man. His replacement is therefore big news.
What makes the news even bigger in Ivanov's case is that he and Putin were believed to be exceptionally close. Ivanov and Putin served together in the KGB in St. Petersburg in the 1970s and have known each other and been close friends for decades. Ivanov's loyalty to Putin - essential for any person occupying this post - is total, and he has sometimes even been spoken of as a possible successor.
Comment: As a commenter on the original Duran article points out, it's not always the place where the position fits in the organization that determines its importance, but the personality who occupies it: "Rather than a demotion of Mr Ivanov, this may be a promotion of the office of special rep for ecology, environment and transport." There are some social media rumors that this might be the case, and that Ivanov will basically be in charge of Russia's involvement in the Silk Road project. We'll have to wait and see.