Written or verbal communications between a lawyer and his client is privileged and confidential. Nobody (especially the opposing side in a lawsuit) can compel the client or lawyer to divulge the contents of the communication. With rare exception even a Court can not compel a lawyer or his client to divulge the contents of a communication between attorney and client. Lawyers must zealously guard attorney – client communications.
The purpose behind the privilege is to encourage open and honest communication between attorney and client. In order to provide effective representation a lawyer and client must be able to communicate honestly and freely about the facts of a case without fear that either will be forced to divulge them. Why? A lawyer needs to know the bad facts so he can deal with them in a way that hopefully minimizes their impact on a case.