Lady Macbeth is evoking the idea that Macbeth will truly not be a man until he commits regicide, this is killing King Duncan. She is basically calling him a coward, LM is manipulating Macbeth into killing the king, she is using her psychological abilities to persuade macbeth into doing this because she doesn't want to do it herself. In the Jacobean era it wouldn't be women like to kill someone. Therefore she persuades Macbeth