"The network is the message"...what does it all mean?

Marshall McCluhan explained (I believe in his book Communication and Empire) that the medium through which a specific message is displayed (i.e. in a letter, in a book, face-to-face communication, over the telephone etc.) controls the meaning of that message. This makes sense, if you think about it, because there are other factors that control understand of a message besides the specific words. The medium through which the message is communicated determines how the receiver interprets and understands that message as they take into account context, body language, tone, presentation, etc. Now that we understand this concept we can take it one step further to apply it to what Castells is talking about when he says "the network is the message" (1). Networks determine how we get and decode messages. It is another medium through which to communicate. However, it is not simply a static medium like those we have used in the past. The networks almost living, breathing organisms in and of themselves (even though I know, I know they don't exist without humans to join them but just bear with me on this for a minute) as they affects the way people interact and socialize. New social structures and communication practices arise from being involved in different networks and this then shapes the way people understand various messages. Take, for example, Facebook. Facebook has completely changed the way people keep in touch over long distances, communicate with friends, and display themselves to the world. It is a social network that has changed what is socially acceptable to showcase about yourself, how you can meet people, and the very way people talk to each other. If you don't have Facebook, you are missing out on key socializing opportunities. In this sense, the network is the message as it shapes meaning and defines who we are as a society and an individual and this is the major change seen from the digital revolution.