The difference in the programming model is that in a message passing language you can define logic around the handling of the message. Usually that logic is not

The difference in the programming model is that in a message passing language you can define logic around the handling of the message. Usually that logic is nothing more than passing to a method, but in some cases you may want to have other behaviour which you can write code to define. The other behaviour is what is absent from languages where methods are implemented as a jump as described by the parent.