First-class messaging implies "encapsulation". A message can not directly modify its target. Its target must INTERPRET the message somehow and then decide what

First-class messaging implies "encapsulation". A message can not directly modify its target. Its target must INTERPRET the message somehow and then decide what to do about it. A message can not modify its target. Only the recipient who receives the message can access its own data, which means its data is "encapsulated". It is as if you sent me a letter by "first class mail". Great I can read your letter. But your letter can not directly alter the arrangement of furniture in my house. Only I can do that. And perhaps when I read your letter I decide to take such action. Or maybe I decide not to.