I really cannot bear an immoral man. I am not a Pharisee, I hope; and I should not have minded his merely doing wrong things: we are none of us perfect. But your father didn't exactly do wrong things: he said them and thought them: that was what was so dreadful. He really had a sort of religion of wrongness. Just as one doesn't mind men practising immorality so long as they own that they are in the wrong by preaching morality; so I couldn't forgive Andrew for preaching immorality while he practised morality. You would all have grown up without principles, without any knowledge of right and wrong, if he had been in the house. You know, my dear, your father was a very attractive man in some ways. Children did not dislike him; and he took advantage of it to put the wickedest ideas into their heads, and make them quite unmanageable. I did not dislike him myself: very far from it; but nothing can bridge over moral disagreement. (1.67)
Lady Brit tells us quite early on that Andrew has his own unique philosophy and set of morals, which altogether create a "religion of wrongness."
Really, Barbara, you go on as if religion were a pleasant subject. Do have some sense of propriety. (1.237)
Lady Brit seems to think it's tacky or improper for her to talk so much about religion, but no one other than her seems to mind.
CUSINS: Excuse me: is there any place in your religion for honor, justice, truth, love, mercy and so forth? UNDERSHAFT: Yes: they are the graces and luxuries of a rich, strong, and safe life. (2.232-233)
This must be that "religion of wrongness" that Lady Brit was talking about at the beginning of the play. It seems that, in Undershaft's view, power and money (particularly the latter) lay the groundwork for the kind of virtues that are traditionally associated with religion.
UNDERSHAFT: Choose money and gunpowder; for without enough of both you cannot afford the others. CUSINS: That is your religion? UNDERSHAFT: Yes. (2.235-237)
When Dolly presses Andrew on his religious views and asks what would happen if he had to choose between his money and gunpowder religion and the more traditionally religious virtues Dolly has just listed (see the previous quote), Andrew says that one should choose money and gunpowder, since without them, there's nothing else. Smart one, Andrew.
CUSINS: Pardon me. We were discussing religion. Why go back to such an uninteresting and unimportant subject as business? UNDERSHAFT: Religion is our business at present, because it is through religion alone that we can win Barbara. (2.260-261)
Neither Andrew nor Dolly is religious in the way that Barbara is (although Dolly has been kind of pseudo-pretending with his faux interest in the Army), but they both want to keep her happy, so it seems they must find a way to reconcile their beliefs and hers—or, more likely, reconcile her to their beliefs.
CUSINS: That doesn't matter. The power Barbara wields here—the power that wields Barbara herself—is not Calvinism, not Presbyterianism, not Methodism— UNDERSHAFT: Not Greek Paganism either, eh? CUSINS: I admit that. Barbara is quite original in her religion. (2.266-268)
Even though Barbara is portrayed as a kind of naïve idealist in a certain sense, Dolly is careful to note that her religion and principles—like her father's—are actually pretty unique to her.
Have you ever been in love with Poverty, like St. Francis? Have you ever been in love with Dirt, like St. Simeon? Have you ever been in love with disease and suffering, like our nurses and philanthropists? Such passions are not virtues, but the most unnatural of all the vices. This love of the common people may please an earl's granddaughter and a university professor; but I have been a common man and a poor man; and it has no romance for me. Leave it to the poor to pretend that poverty is a blessing: leave it to the coward to make a religion of his cowardice by preaching humility: we know better than that. We three must stand together above the common people: how else can we help their children to climb up beside us? Barbara must belong to us, not to the Salvation Army. (2.285)
Once again, Andrew preaches that morals and religion should be adopted and shaped according to one's circumstances. Although he (kind of) admits that it's okay for some people to revere poverty and humility, he does not think that he or Dolly (or his daughter) should have any part of that, since they "know better." Their religion, he contends, has to result in getting power that they can then use to help others.
How are we to feed them? I can't talk religion to a man with bodily hunger in his eyes. [Almost breaking down] It's frightful. (2.329)
Barbara actually seems halfway to her father's point of view here, since he argues that bribing people with food/bread isn't actually an honest conversion. As Barbara herself says here, how can anyone concentrate on religion when they're hungry?
Look at poor little Jenny Hill, the Salvation lassie! she would think you were laughing at her if you asked her to stand up in the street and teach grammar or geography or mathematics or even drawing room dancing; but it never occurs to her to doubt that she can teach morals and religion. You are all alike, you respectable people. You can't tell me the bursting strain of a ten-inch gun, which is a very simple matter; but you all think you can tell me the bursting strain of a man under temptation. You daren't handle high explosives; but you're all ready to handle honesty and truth and justice and the whole duty of man, and kill one another at that game. What a country! what a world! (3.125)
We might sometimes find Andrew's views regarding power and morality a bit hard to swallow or even cynical at times, but he makes an excellent point here: How is it that people are so willing to claim knowledge of what constitutes morals and religion, to the point of being able to teach others? It's an interesting question that we don't ask enough.
After all, my dear old mother has more sense than any of you. I felt like her when I saw this place—felt that I must have it—that never, never, never could I let it go; only she thought it was the houses and the kitchen ranges and the linen and china, when it was really all the human souls to be saved: not weak souls in starved bodies, sobbing with gratitude for a scrap of bread and treacle, but fullfed, quarrelsome, snobbish, uppish creatures, all standing on their little rights and dignities, and thinking that my father ought to be greatly obliged to them for making so much money for him—and so he ought. That is where salvation is really wanted. My father shall never throw it in my teeth again that my converts were bribed with bread. [She is transfigured]. I have got rid of the bribe of bread. I have got rid of the bribe of heaven. Let God's work be done for its own sake: the work he had to create us to do because it cannot be done except by living men and women. When I die, let him be in my debt, not I in his; and let me forgive him as becomes a woman of my rank. (3.422)
Barbara has finally decided to come over to the "dark side," but she seems to feel like she's doing it on her own terms…and perhaps based on beliefs that she had already held. She had already remarked earlier on the difficulty of doing the spiritual work of the Army when her target demographic was hungry and miserable (i.e., probably focused more on survival than spiritual fulfillment), and now she'll get the opportunity to play to well-fed, well-paid workers in her father's factory. She seems just as enthusiastic and pious as ever, so it seems like she might not have changed that much after all…even after revising her principles pretty heavily.