Just read a review on this that pretty much analyzed the movie as the third part of PTA's unofficial trilogy on American capitalism and religion in the 20th century.
There Will Be Blood depicts the rise of America at the turn of the century, shaped strongly by religion and capitalism, but only one can win out to be the dominant factor and in the end it's capitalism, the greed of man, that beats out the nation's need for spirituality.
The Master shows America in its 'glory days' post WW2 as the American dream come to life, a job, a family and a house available for everyone, a capitalist utopia, but it's all fluff and people who don't fit into the narrative wander aimlessly in search for something new to believe in, which new capitalist entrepreneurs will gladly sell to them in the form of new religions.
Inherent Vice shows America on the decline, the entire nation has become disillusioned by the Vietnam war, an ugly, where morality is gone, the American Dream is a lie and the misfits of society have detached themselves from this reality through drugs, their new religion that ironically has also become the cornerstone of American capitalism in decay.
Reading shyt really made me want to rewatch all three movies again ASAP.