I believe this phrase means that we need to pay more attention to what our message is going to impact, how it is going to impact us and how it is going to be delivered to us. The content of the medium is always another medium. When new technology comes out, it changes society structurally and psychologically. As technology progresses and changes, society changes as well. Just think about what the radio or tv did. And now we have the newest devices just falling onto our laps. Though the information (message) may stay the same, the way it is delivered (media) changes.
