The answer to this thought posed by Mcluhan is not always completely clear or comprehended by most people.
From my reading on this topic I understand that the message is the medium or furhtermore the way the medium affects the way we interact with others and our surroundings rather than the content of the message that we digest, while not exactly the same, i like to look at similar to how we view the journey as the destination. Whether this medium is transferred orally via radio or visually via text on a screen, the way in which we engage with a medium has a profound influence on our lives.
Once people read newspapers in the public sphere at places like cafes and train stations and gathered information not only via the text and images presented on the paper but in a social way by interacting with the the medium itself and interacting in a unique way with the world around us. To help illustrate my point, think about how often a person on a train might ask a person holding a newspaper if they could see the sport section, or use the paper afterwards or even make an enquiry about a certain article. The medium in this case creates the message of provoking social thought and discussion about news and events. In this way we might argue that when people engage with news and events on personal devices such as computers and smartphones, the potential for further discussion with others is limited because we are engaging with content in a much more a private way.