There is no doubt that Monty Python is one of the greatest geniuses of comedy. Between a TV series and three movies they have produced an incredible range of work and indeed some hilarious material. There is also no doubt they can spark quite a bit of controversy, and nowhere is that more evident than in their second feature film Life of Brian. This is a hilarious movie in itself, but it does have some deeper meanings compared to Monty Python and the Holy Grail and Monty Python's The Meaning of Life.
The plot of Life of Brian can be summed up quite simply as one man's ongoing quest to be left alone. Graham Chapman plays the role of Brian, an ordinary fellow who just happened to be born in a stable next door to the Nativity. He grows up to be a respectable young man who finds himself joining one of several anti-Roman groups in the hopes of helping his people, but that eventually leads to unforeseen consequences, and he spends much of the movie either running away from both the Romans and the hoard of people irrevocably convinced that he is their messiah.
Of course, given the movie is obviously influenced by Biblical epics such as Ben-Hur it is natural that it generated a lot of controversy when it was initially released. It is not a story about Jesus, nor any other religious figure, but it clearly draws inspiration from those stories, and in doing so provides a satirical commentary on how religion can affect people, as is especially noteworthy in the scenes with Brian's "followers".
This massive crowd of people that we see is stubbornly convinced that Brian is their messiah (when in fact he really just wants to be left alone), but they take that idea at face value and just assume they're always right. In fact, they never even really bother to listen to their supposed messiah. When Brian tries to tell them to go away, they just declare that "a blessing". When he tries to explain that he is not the messiah, the crowd just makes up an excuse in response like "I'll say you are, and I should know. I've followed a few." or "Only the true messiah denies his divinity."
That in itself is frustrating enough, especially when the whole crowd shows up at his house. There Brian tries to tell them to think for themselves. They say they agree, but the fact that every single one does so in unison seems to suggest otherwise. Even his overbearing mother telling them to go away is seen as "a blessing", leading to one of the best lines in the movie ("He is not the messiah, he is a very naughty boy!")
The movie also emphasizes the inevitable conflicts people can end up in when driven by blind faith. How many people have died over disagreements about religion throughout history? We see the absurdity of such disagreements happen throughout the movie. They do allude to it on a few fronts, with one good example being the fact that the various anti-Roman groups who all have very similar names (Judean Peoples' Front, Peoples' Front of Judea, etc.) and more or less the same goal (getting rid of the Romans) seem to spend more time fighting against each other than actually doing anything about the authorities they supposedly oppose. One of the more obvious examples, of course, is in Brian's "followers". Brian loses a shoe, and upon finding it they immediately interpret it as a sign, but can't agree on what it means. Then they become divided over whether they should "follow" the gourd or the shoe.
Finally, we see the violence that comes with blind faith. How many "peaceful" religions have committed horrible atrocities. The scene with the Hermit brings this aspect to the forefront. After getting annoyed with all the trouble Brian's "followers" are causing him, he starts to take out his anger on Brian himself. One of the "followers" tries to tell him he's the messiah, to which the Hermit replies "no he's not". The immediate reaction of course is to "kill the heretic". The part that really ties it all together is the hypocrisy of these "followers", who proceed to drag the Hermit away to have him killed all the while ignoring their own supposed messiah's pleas to leave the poor guy alone.
How many of these concepts could be applied to actual religions in the world? Quite a lot I'd say. Life of Brian is a hilarious movie with lots of great moments, but underneath all that great humor is a strong social commentary on just how far people will go for their beliefs.