"People talk about the conscience, but it seems to me one must just bring it up to a certain point and leave it there. You can let your conscience alone if you're nice to the second housemaid"

Henry James is suggesting that a person must not overthink their conscience. It is necessary to have a conscience and to be aware of it, however it is not required to continuously be questioning it. Rather, one must be kind and considerate to others, and this ought to be enough to please one's conscience. This is specifically true when it pertains to those who are less lucky, such as the second housemaid. By being good to her, one can be sure that their conscience remains in check. This quote is a tip that it is necessary to be kind and thoughtful to others, which this suffices to satisfy one's conscience.