Morality is a huge topic for the play's characters; every time you turn around, someone is getting all philosophical about the difference between right and wrong—and usually getting ruffled about someone else's opinion in the process. The "Big Bad Wolf"—as far as morality goes—is Andrew Undershaft…at least, for most of the play. Why, you ask? Well, because he's grown rich off of selling weapons to the highest bidder and plans to continue the Undershaft family tradition of skipping over its own heirs and leaving the business to a foundling. In Lady B's eyes, all of the above make him a profoundly immoral person.
Andrew ends up poking holes in his wife's notion of morality by the end of the story, though. He finds a lot of hypocrisy and contradictions in his family's notions of "right" and "wrong," and makes the case for why what he does is "right"…well, at least for him.
For all its talk about morality, the play doesn't end up being all that concerned with it—the message really is just that people shouldn't let arbitrary conceptions of right and wrong cloud their awareness of reality or the conditions that surround them.
The play ultimately shows Andrew Undershaft to be the most profoundly moral dude in the bunch, since he refuses to participate in a lot of the hypocrisies that more traditionally "moral" people buy into.
There's a lot of interesting "battle of the sexes" stuff going on in this play. When we first meet the characters, Lady Brit clearly rules the roost, which seems a bit unorthodox given the time period. However, all that changes when her estranged husband comes back into the picture (albeit at her request). The family goes from being a matriarchy to a firm patriarchy in the blink of an eye, and Lady Brit butts up against the reality that her husband really has all the power in their marriage by virtue of his wealth (and his gender doesn't hurt, either, of course).
Then there's the transition that Barbara makes from being an empowered "major" to a girl-like creature who clutches at her mother's skirts and begs for advice on how to buy a house—there's definitely something significant going on with Shaw's presentation of gender there as well.
There's a lot of room for debate or interpretation in the journeys the female characters take, but it seems pretty clear that feminism isn't exactly the play's primary concern . . .
Through the character transitions of Barbara and Lady Brit, in which both women basically end up "defanged" and far less powerful than they start out, Major Barbara actually ends up being pretty anti-feminist in its presentation of women.
By maintaining her individuality and commitment to her cause (with some adjustments here and there), Barbara ends up being a powerful figure and, as such, a kind of feminist one.
In this play, our protagonist, Andrew Undershaft, makes weapons for a living and sells them to the highest bidder (regardless of whether they're friends or foes), and his family has a big problem with that. So, the ethics of enabling war and violence come up a lot in conversations among the family. According to people like Lady B and Barbara, it's immoral to facilitate violence and death—and then to get rich off of it—but in Andrew's attitude it's pretty different (obviously). By the end of the play, he's actually gotten some of the others to agree with him that making weapons for those around the world who need them might just be the most moral thing to do after all.
The play essentially turns Barbara's moral universe upside down by the end. Her morality, which assumes that violence is wrong and must be discouraged/prevented, is rejected in favor of Andrew's view that violence is a necessary and unavoidable part of life—and the most moral thing to do is recognize and respond to that reality.
The violence and aggression we see among the poorer characters—and particularly directed against women—highlights a hypocrisy in the Army's stance: the Army might be against war and violence and disdain the rich, but poverty actually leads to just as much violence . . .
In this play (as in life), money and the desire for it are pretty important motivators. Whether Barbara or her mother are happy about it, wealth and money are crucial to their objectives and overall lives. Lady B basically admits as much at the beginning when she has to resign herself to asking Andrew for more money to support the girls as they prepare to get married. Barbara is a bit more reluctant to admit how much money drives even what she does, but she gets a wake-up call when the Army enthusiastically accepts money from her father and a whisky distiller—i.e., two people whose businesses, in her view, contribute to the nasty things the Army is trying to combat. Ultimately, the characters are kind of forced to admit that they need wealth, for better or worse, and it's not really something to be treated as inherently worse than poverty . . .
Wealth and poverty are inherently neither good nor bad in the play's universe—but if one is to be pursed/encouraged as part of a "moral" life, it's wealth. That's Undershaft's view, and it seems to be holding sway over basically everyone else toward the end.
Undershaft considers poverty inherently evil because money/wealth—i..e, stability—are absolutely necessary for allowing virtue to exist/flourish.
Given that we have a character named Lady Britomart, you know from the get-go that discussions of class and society with a capital "S" are going to be part of the mix. Lady B fancies that she's not a snob like the rest of her family, but she does have some definite ideas about how people in her family's class should be acting.
Barbara does, too. Even though she's happy to live the lifestyle of a pauper when we first meet her, she is very keen on avoiding "middle-class" ideas about morality—and, ultimately, decides that her morals and principles must match those of her class. What does that mean? Well, read on . . . but the big takeaway here is that class is a big deal, whether the characters want to admit it or not.
Lady Brit is not a snob—we know because she's very accepting of her future son-in-law, Dolly, who is a professor of Greek and a foreigner—i.e., not of the same class as her family.
Lady Brit is totally a snob—and a hypocrite; if Andrew had been willing to let Stephen take over the business and act according to the rules of their class (rather than going outside the class/family for an heir), her objections to his "immoral" profession would have disappeared pretty quickly.
Well, one thing's for sure: love him or hate him, Andrew Undershaft really tries to avoid being a hypocrite. Sure, his morals seem a bit topsy turvy to the other characters (and maybe to the reader as well) since as far as he's concerned, his moral obligation is to be rich and make and sell lots of weapons so that the good and bad elements of the world alike can have a fair fight. People like Lady B and Barbara find these ideas troubling, because it means that he's enabling violence and kind of giving into greed, which is bad according to traditional Christian values. By the end of the play, though, we can kind of see where Andrew is coming from; in his view, violence is going to exist regardless, and wealth is better than poverty, so why should he take a stand against either?
Well, the sustainability of Undershaft's morality is debatable (and dealt with elsewhere in "Themes"), but it's important to notice how the actions of supposedly more "moral" people end up supporting or facilitating all kinds of bad behavior (like lying or violence). Also, these people are often dependent on the "immoral" for financial support, and don't even blink before asking for and accepting that help—which seems more than a little hypocritical. So yeah, by the end, Undershaft looks just about as moral as everyone else, if not a bit more so, since he does his best to avoid and challenge hypocrisies.
Shaw includes a lot of relatively benign moments in which Lady B contradicts herself to clue us into the fact that she really is just a big honking hypocrite at heart—as we learn when she's willing to accept more money from Andrew, even though she doesn't approve of how he earned it at all.
As far as Andrew is concerned, being a hypocrite is far worse than being "immoral"—so, even if his ideas run against the dominant "morality," his willingness to call out hypocrisies and contradictions for what they are—to live in reality, that is—make him one of the most moral characters in the play.
The whole idea that the meek will inherit the earth is not part of Andrew Undershaft's philosophy—he's all about power and the things that get it for you (like money and weapons). Hey, there's a reason that people thought Shaw was influenced by Nietzsche, right?
Undershaft makes no apologies for wanting power, as it prevents others from having to take care of him. He's not the only character who likes power and desires control either—Barbara is also a force to be reckoned with, and you could argue that she manages to hold on to her convictions despite heavy assault from her father (although she does end up revising them a bit). And of course, Lady B relishes being in control, though she loses a lot of power in the end . . .
Anyway, TL;DR: the characters are super interested in power in all of its forms and how to maintain it.
Barbara starts out being a powerful figure, but ultimately her father and his philosophies completely overshadow her and her religion, leaving her with entirely revised principles and acting like a virtual baby at the end of the play.
Barbara shrewdly treats her father's philosophies and religion as a kind of à la carte deal, taking what she likes and using it to further her aims. Although her father enables it—that much is true—you can't deny that she is still pursuing exactly the same aims and holds the same religious ideas that she had at the beginning . . . now she just has a better way to execute them.
Barbara is a Major in the Salvation Army, and she remains fervently religious and devoted to the cause of conversion for most of the play. However, her father pits his own wacky set of morals and philosophical/religious views against Barbara's, challenging a lot of her assumptions about religion and the best way to spread it to others/help the cause of belief. They probably still have pretty radically different views at the end, but the dialogue at least helps Barbara separate herself from some of the hypocrisies and misconceptions that her father believes were standing in her/the Army's way.
Ultimately, the play suggests that everyone can have their own religion or set of morals that is particular to them—well, if the character development for Barbara, Undershaft, and Dolly is supposed to be any indicator.
Andrew's suggestion that there can be different religions is disingenuous, since he ultimately expects everyone to come over to his utilitarian way of thinking about right and wrong, wherein right and wrong are determined according to what is useful to you.