How we cite our quotes: (Act.Line)
Quote #4
UNDERSHAFT: From the moment when you become Andrew Undershaft, you will never do as you please again. Don't come here lusting for power, young man.
CUSINS: If power were my aim I should not come here for it. You have no power.
UNDERSHAFT: None of my own, certainly.
CUSINS: I have more power than you, more will. You do not drive this place: it drives you. And what drives the place?
UNDERSHAFT [enigmatically]: A will of which I am a part. (3.295-299)
Andrew has been playing up the importance of power and how much he has, but here he kind of contradicts all those statements by suggesting that you don't really have any power of your own once you become Andrew Undershaft—and Dolly concurs, suggesting that the products/production themselves drive everything.
Quote #5
UNDERSHAFT: Not necessarily. Remember the Armorer's Faith. I will take an order from a good man as cheerfully as from a bad one. If you good people prefer preaching and shirking to buying my weapons and fighting the rascals, don't blame me. I can make cannons: I cannot make courage and conviction. Bah! you tire me, Euripides, with your morality mongering. Ask Barbara: she understands. [He suddenly reaches up and takes Barbara's hands, looking powerfully into her eyes]. Tell him, my love, what power really means.
BARBARA [hypnotized]: Before I joined the Salvation Army, I was in my own power; and the consequence was that I never knew what to do with myself. When I joined it, I had not time enough for all the things I had to do. (3.302-303)
Andrew is getting tired of Dolly's teeth gnashing about the morality of joining the Undershaft's business. So, he gets Barbara thinking about what she recently learned about power, which he thinks will help convince Dolly.
Quote #6
BARBARA: Yesterday I should have said, because I was in the power of God. [She resumes her self-possession, withdrawing her hands from his with a power equal to his own]. But you came and shewed me that I was in the power of Bodger and Undershaft. Today I feel—oh! how can I put it into words? Sarah: do you remember the earthquake at Cannes, when we were little children?—how little the surprise of the first shock mattered compared to the dread and horror of waiting for the second? That is how I feel in this place today. I stood on the rock I thought eternal; and without a word of warning it reeled and crumbled under me. I was safe with an infinite wisdom watching me, an army marching to Salvation with me; and in a moment, at a stroke of your pen in a cheque book, I stood alone; and the heavens were empty. That was the first shock of the earthquake: I am waiting for the second. (3.305)
At her father's prompting to remember what she's learned about power, Barbara basically recounts her realization that, instead of being "in the power of God" when she was with the Army, she was actually in the power of her father and the whisky distiller Bodger…you know, corporate interests. So, it seems that this is the answer that Andrew was looking for? The idea seems to be that Dolly is (like everyone, really) already in the sway of the Undershaft fortune, so he might as well work for it outright. If you can't beat them, join them.