Message is a precise encapsulation of a position or idea. "Message" takes its original form from the metaphor of communication being personal: someone is moved when they feel they are being spoken to directly, as in "send them a message" or "if you want to send a message, use Western Union."
In the era of mass broadcasting, creating message while still being generic enough to be widely disseminated became the focus of political advertising.
In the present message is most effective when ordinary people want to retransmit that message. This means that attaching message in the form of a meme - which people want to spread - is part of the dynamics of political discourse. (See Viral Marketting).