Messaging is the clarification of value using words, images, and other contextual hints, in order to impact how people think or feel about a brand, its products, or just its projects and initiatives.
If it doesn’t affect or reinforce positioning, it’s not messaging.
Also see Positioning, Brand Messaging, Copy, Propaganda, and Strategic Narrative
Messaging is creative Positioning; whereas positioning is an idea, messaging is acting on that idea, which in turn refines the positioning itself.
Messaging is a creative activity whereas propaganda is the propagation of already-minted messages