The matron's opinion of Rosanna was (in spite of what she had done) that the girl was one in a thousand, and that she only wanted a chance to prove herself worthy of any Christian woman's interest in her. My lady (being a Christian woman, if ever there was one yet) said to the matron, upon that, 'Rosanna Spearman shall have her chance, in my service.' (18.104.22.168)
The ideas of second chances, forgiveness, and redemption are closely linked to the theme of religion. Lady Verinder, as a "Christian woman," is willing to give Rosanna a second chance in spite of her past as a thief.
'And I desire that my […] sister may be informed, by means of a true copy of this, the third and last clause of my Will, that I give the Diamond to her daughter Rachel, in token of my free forgiveness of the injury which her conduct towards me has been the means of inflicting on my reputation in my lifetime; and especially in proof that I pardon, as becomes a dying man, the insult offered to me as an officer and a gentleman, when her servant, by her orders, closed the door of her house against me, on the occasion of her daughter's birthday.' (22.214.171.124)
We're meant to believe that Lady Verinder is sincerely "a Christian woman" when she gives Rosanna a second chance. But John Herncastle's Will, in which he claims repeatedly that he forgives his sister for the "insult" of not inviting him to Rachel's birthday party, is meant to sound insincere. After all, he knew that the Indians were after the Moonstone and that it would be dangerous for Rachel to be in possession of it. This is the first example of a character using religion for hypocritical, self-serving reasons in this novel.
(Nota bene: I am an average good Christian, when you don't push my Christianity too far. And all the rest of you—which is a great comfort—are, in this respect, much the same as I am.) (126.96.36.199)
Gabriel Betteredge compares his own religion to the reader's: he says that everyone is basically good, as long as you don't push them too far.
She handed me back the tract, and opened the door. We must sow the good seed somehow. I waited till the door was shut on me, and slipped the tract into the letterbox. When I had dropped another tract through the area railings, I felt relieved, in some small degree, of a heavy responsibility towards others. (188.8.131.52)
Penelope is not interested in reading the religious tract Miss Clack offers her. But Miss Clack can't just let it go. She shoves the tract through the mail slot on her way out, and insists that it's part of her "heavy responsibility towards others." It's not that the other characters are not Christian; Miss Clack just thinks that her own version of Christianity is far superior to others.
Oh, my young friends and fellow-sinners! beware of presuming to exercise your poor carnal reason. Oh, be morally tidy. Let your faith be as your stockings, and your stockings as your faith. Both ever spotless, and both ready to put on at a moment's notice! (184.108.40.206)
Miss Clack preaches to the reader against using "reason" or intellect in solving problems. This is obviously questionable advice. The next piece of advice, in which she compares religious faith to "stockings," isn't just an odd simile. She suggests that her "faith" isn't something that she "wears" at all times – it's something that she can "put on at a moment's notice." This is strange: does that mean that her devout religious faith is something that she can "put on" and turn off? Is she letting slip that it's all a show?
He beamed on us with his beautiful smile; he held out a hand to my aunt, and a hand to me. I was too deeply affected by his noble conduct to speak. I closed my eyes; I put his hand, in a kind of spiritual self-forgetfulness, to my lips. He murmured a soft remonstrance. Oh, the ecstasy, the pure, unearthly ecstasy of that moment! I sat—I hardly know on what—quite lost in my own exalted feelings. When I opened my eyes again, it was like descending from heaven to earth. There was nobody but my aunt in the room. He had gone. (220.127.116.11)
Miss Clack's "ecstasy" seems more than religious in this passage. It seems like it's not just "spiritual self-forgetfulness" when she kisses Godfrey's hand. Sounds to us like she's got a major crush and she is trying to disguise it by calling it religiously "exalted feelings."
Sorrow and sympathy! Oh, what Pagan emotions to expect from a Christian Englishwoman anchored firmly on her faith! (18.104.22.168)
Most "Christian Englishwom[en]" wouldn't think it was "Pagan," or ungodly to feel "sorrow and sympathy" when they find out that their aunt is dying. But Miss Clack claims that she's happy at the news because she'll be able to guide her aunt in her last days to become a better Christian. Of course, the way she says it suggests that she's really only excited by the idea that her aunt might leave her money when she dies.
[Mr Bruff] is the family solicitor, and we had met more than once, on previous occasions, under Lady Verinder's roof. A man, I grieve to say, grown old and grizzled in the service of the world. A man who, in his hours of business, was the chosen prophet of Law and Mammon; and who, in his hours of leisure, was equally capable of reading a novel and of tearing up a tract. (22.214.171.124)
Miss Clack thinks that Mr. Bruff is too obsessed with "worldly" or non-spiritual things. He is motivated by "Law and Mammon" ("Mammon" means "money" or greed).
Rachel and I went alone together to church. A magnificent sermon was preached by my gifted friend on the heathen indifference of the world to the sinfulness of little sins. For more than an hour his eloquence (assisted by his glorious voice) thundered through the sacred edifice. I said to Rachel, when we came out, 'Has it found its way to your heart, dear?' And she answered, 'No; it has only made my head ache.' (126.96.36.199)
Miss Clack says that she feels exalted by the "thunder[ous]" voice of the minister. But Rachel only gets a headache. Which of them is the reader supposed to sympathize with?
'Oh, Rachel! Rachel!' I burst out. 'Haven't you seen yet, that my heart yearns to make a Christian out of you? Has no inner voice told you that I am trying to do for you, what I was trying to do for your dear mother when death snatched her out of my hands?' (188.8.131.52)
Miss Clack finally lets the cat out of the bag: she tells Rachel that she wants to "make a Christian out of" her. Of course Rachel would be offended by this –after all, she's already a Christian. But what really offends her is that Miss Clack suggests that her dead mother, Lady Verinder, has gone to hell because Miss Clack didn't save her soul in time. To Rachel, this is both offensive and ridiculous, since her mother was a good, kind woman her whole life.