They always think they can improve upon Nature and mend what God has made. (10.18)
Many events in this book lament the evil of men who treat animals with cruelty. Here, this kind of cruelty is compared to "playing God"—daring to change something God has made. It's the worst kind of offense, and the theme of power and how it can be abused is something that comes up repeatedly in this story.
Master said, God had given men reason, by which they could find out things for themselves; but He had given animals knowledge which did not depend on reason, and which was much more prompt and perfect in its way, and by which they had often saved the lives of men. (12.15)
When Beauty saves John Manly and Squire Gordon from driving across a broken bridge, Beauty tells us what Squire Gordon says afterward, which is basically that God's gifts to horses saved them all. It's an indirect way of thanking God for their survival, and it shows that Squire Gordon sees a connection between religion and the natural world.
Why don't they cut their own children's ears into points to make them look sharp? […] What right have they to torment and disfigure God's creatures? (10.9)
Here's a good example of how this story talks about animals in relation to Christianity: Horses and other animals are considered God's creatures. So changing their physical appearance on a whim is not only cruel, it goes against God's intentions. Pretty awful any way you think about it.
There is no religion without love, and people may talk as much as they like about their religion, but if it does not teach them to be good and kind to man and beast, it is all a sham […]. (13.11)
This passage comes from a chapter called "The Devil's Trade Mark," where John Manly and James are discussing a boy who's cruel to his horses. They talk for a long time about cruelty, calling it the "devil's trade mark" (hence the chapter title), and end with a long rant about love, God, and religion. Here, John agrees with James, telling him that anyone who says they're religious but acts cruelly is not really religious at all because love is at the foundation of all religion. Heavy stuff for a conversation in a stable.
They are like children; train 'em up in the way they should go, as the good book says, and when they are old they will not depart from it, if they have a chance, that is. (15.5)
The old ostler Beauty encounters at an inn talks for a long time about the proper care of young horses. Here his reference to the "good book" makes it clear that he's a pious man, and his attitude about horses makes it even clearer that he's a good man, too.
"I have heard the commandments read a great many times, and I never noticed that any of them said, 'Thou shalt be rich.' And there are a good many curious things said in the New Testament about rich men that I think would make me feel rather queer if I was one of them." (35.43)
Ah, Jerry Barker. Now we're in the part of the book where religion is a particularly strong theme, because Jerry is not only a very kind man, he's a very religious one. We can tell this from the very first chapter about Beauty's life with Jerry, since Jerry starts quoting the Bible right away. This is just the first of many quotes and references to religion during Beauty's stay with Jerry.
"Real religion is the best and truest thing in the world and the only thing that can make a man really happy, or make the world any better." (36.24)
One of Jerry's conflicts is that of working on Sunday: He's offered a job to drive his cab on Sunday, but refuses, even though it means turning down money he really needs. He explains his reasons at great length, but the bottom line is that he believes religion is the best thing in the world. He says it very plainly in this particular quote.
"[…] I don't see that your religious people are any better than the rest."
"If they are not better," put in Jerry, "it is because they are not religious. You might as well say that our country's laws are not good because some people break them." (36.24)
For Jerry Barker, not only is religion the best thing in the world—it turns out that religious people are actually better than everyone else. And by religious, Jerry means the people who actually follow the teachings of Christianity. At least he's honest about his opinions.
"Why, Polly, you are as good as the minister, and so, as I've had my Sunday morning sermon early to-day, you may go and tell Dinah that I'll be ready for her as the clock strikes ten." (37.12)
High praise from Jerry Barker to his wife, here: Her argument for why he should drive his cab to help a friend whose mother is ill is apparently good enough to be a sermon. This chapter illustrates how someone like Jerry can be observant and religious while skipping church. He finds a moral lesson in his wife's lecture, and when he drives to the country later, he spends an afternoon outdoors, appreciating nature in a way that almost feels sacred.
"We have no right to distress any of God's creatures without very good reason." (46.21)
During the most difficult time in Beauty's life, he still encounters good, moral people who try to help him out. Here, a woman who finds Beauty strapped to a cart with a bearing rein urges Beauty's master to let the rein out, reminding the man that horses are God's creatures—and reminding the reader, too.