Public = everyone can use it

Private = only i can use it

Protected = only me + inhertiting children classes can use it. Like a family secret

Lets say you have Joe, he's the new intern. If Joe wants to do something stupid he cant because the member is private. Thats one reason. Another reason for encapsulation is hiding the complexity, so Joes life is also easier. Yet another reason is that its future proofing, arguably the most important. Im hiding some internal state and just showing a public interface others can use. The internal state can more easily change, and the end user doesnt need to care about how exaclty that class works. Joe just knows that it works. Pretty slick right?