Alyssa argues that The Master isn't about the Super Adventure Club, but faith more broadly (spoilers below):

“If you find a way to live without a master, without any master, let us know,” Dodd tells Freddie as his acolyte tries to decide to vanish into the Cause forever or be cast out. “You’d be the first person in the history of the world.” It’s not a subtle line, but it is, intriguingly, contradicted by what follows. Freddie goes out into the world, into a bar, where he asks a young woman not if she wants to fuck, but if she’ll have a drink with him. They end up in bed, and as pillow talk, Freddie turns to the questions Dodd asked him in their first processing session so long ago. It’s an odd moment, but surprisingly, sweetly, his ploy, the only resource Freddie has, works.

I don’t know that I trust that in five years, Freddie won’t be dead of drink, by violence, or his own hand. But in this moment, the Cause has given Freddie what he needs to fulfill Dodd’s promise that “What we will do now will urge you towards existence in a group, society, a family.” Dodd has it wrong: the true test of a faith is whether it can live and thrive in the soil of human experience, beyond the watchful eye of prophet or martyr or Master. But Freddie also proves him right. For this one terribly damaged man, the Cause has given him, if only for an afternoon, the thing he needs to live.

Scott MacDonald nods:

Unlike the preacher Eli in "There Will Be Blood," Dodd believes his own bunk (or seems to anyway), and if [director PT] Anderson doesn't respect the belief, he respects the urge to believe. The few times we hear open skepticism of The Cause, the naysayers are depicted the way Dodd might see them: puny, ineffective, smug. They may be right to doubt Dodd, Anderson seems to be saying, but they're wrong to settle for mundane non-belief.