You should take a look at the Reactive Manifesto [1] and the actor model [2]. My own personal and non-expert take is that message orientation is about the wholeness of the actors that pass messages. "Would you care for a drink?" is message oriented. Whereas many systems built on function calls are more like you jabbing me in the butt with a syringe filled with 20 ccs of alcohol.

[1] http://www.reactivemanifesto.org/

[2] http://www.infoq.com/news/2014/10/intro-actor-model