Interesting contrast between Henry and Mary in this chapter. They are using similar manipulation/lies and working for a similar end, but Henry knows the enormity of what he is doing while Mary seemingly does not. I wonder if the upcoming breakup with Edmund will get through to her, or if she will deem him overly priggish and continue believing herself in the right. At this point I'm not sure even Henry taking Fanny's advice and turning to God would make an impression on Mary; she would just think it a last-ditch attempt to influence Fanny.
I do hope Henry takes Fanny's advice. I keep thinking of the verse you included at the start of the story. Doing what is right is terribly hard even when, like Fanny, you have a lifetime habit of doing so, so how much more difficult for Henry who is trying to change himself. He is correct that he can't do it on his own, and I'm glad Fanny didn't take on the flattering task of reforming him, or fall for his other lies.
Kudos to Edmumd for remaining skeptical even under Henry's manipulation. Also glad to see him recognizing Mary's lack of principles a little, even if full enlightenment isn't there yet.