Calling a method on an object is a kind of message passing - please take those arguments here, do your thing with them and send me back whatever return value yo

Calling a method on an object is a kind of message passing - please take those arguments here, do your thing with them and send me back whatever return value you calculated. This really is just a synchronous exchange of two messages between the caller and the callee (plus you also give your processor to the callee to do his work because while you are waiting for the response you don't need it anyway).