Encapsulation means as much as shielding. Each OO object has a shield around it. Objects can't 'see' each other. They can exchange things though, as if they are interconnected through a hatch.

coffee protocol, an example of encapsulation Customer, waiter and kitchen are three shielded objects in the 'cup of coffee' example. Customer and kitchen do not know each other. The waiter is the intermediary between those two. Objects can't see each other in an Object Oriented world. The 'hatch' enables them to communicate and exchange coffee and money.

Encapsulation keeps computer systems flexible. The business process can change easily. The customer does not care about the coffee brew process. Even the waiter does not care. This allows the kitchen to be reconstructed, is only the 'hatch' remains the same. It is even possible to change the entire business process. Suppose the waiter will brew coffee himself. The customer won't notice any difference.

Encapsulation enables OO experts to build flexible systems. Systems that can extend as your business extends. Every module of the system can change independantly, no impact to the other modules.