"The Boondock Saints" has a more complex meaning then most critics give it credit for. Many reviews said that this movie was just a typical "guy movie" with gore, cussing, and violence, but there is much more to it. The idea of taking the law into your own hands, or vigilantism, is a main theme of this movie. Also characterization is related to the theme of the movie. The brothers have a reason for what they're doing, not killing just for fun or revenge. The point in the film when the McManus brothers realized they should take the law into their own hands was in a scene at the police station. They were sleeping there after they finished the questioning about the two men they killed in self-defense. It was clear they were having a dream with the voices in the background and they sprang up from a dream with water dripping on them. The water symbolizes a baptism towards their new mission about to begin. They looked at each other knowing what the other was thinking. .
They realized the best way to rid the city they love from evil was to kill the bad guys themselves. Murphy said, "evil man, dead man." The idea that murderers and mobsters get out of jail on bail didn't seem right to them. This caused instant commotion in the city. When they killed two Russian mafia members, the newspaper called them saints. Ironically enough, the boys had a picture of a saint tattooed on their necks. It's symbolic that they show the world their faces in a courtroom. Courtrooms are a place where justice is served, but that hasn't been the case recently. There were many cases in which people who should have been in jail got off based on how rich they were or who they know. So it's fitting they take care of the main Italian mob boss in the courtroom. He gets the justice he deserves in a courtroom, like the way it's meant to be. .
The brothers are religious people, they aren't bad guys and don't kill just for fun.