Religion
Dr. Thurman: Do you feel alone right now?
Donnie: Oh, I don't know. I mean, I'd like to believe I'm not, but I just... I've just never seen any proof, so I... I just don't debate it anymore, you know? It's like I could spend my whole life debating it over and over again, weighing the pros and cons. And in the end, I still wouldn't have any proof. So I just... I just don't debate it anymore. It's absurd.
Dr. Thurman: The search for God is absurd?
Donnie: It is if everyone dies alone.
Dr. Thurman: Does that scare you?
Donnie: I don't want to be alone.
Donnie: Oh, I don't know. I mean, I'd like to believe I'm not, but I just... I've just never seen any proof, so I... I just don't debate it anymore, you know? It's like I could spend my whole life debating it over and over again, weighing the pros and cons. And in the end, I still wouldn't have any proof. So I just... I just don't debate it anymore. It's absurd.
Dr. Thurman: The search for God is absurd?
Donnie: It is if everyone dies alone.
Dr. Thurman: Does that scare you?
Donnie: I don't want to be alone.
Religion is another major theme in the film. Not in the sense that it is trying to preach a certain gospel, but rather the questioning of faith. Most of Donnie's conversations happen with either his therapist (D. Thurman) or his science teacher (Professor Monnioff). The conversation above is with his therapist, in which Donnie reveals his views on God. He, as Dr. Thurman tells him, is an Agnostic, in that he does not believe in God, but does not deny the possibility that God could exist:
Religion is based on faith, that is the doctrines must be taken on faith. Ultimately there is no concrete, indisputable evidence for any form of faith or deity at the end of the day, so one with faith has to ultimately acknowledge this. Donnie experiences an event where he sees strange water-looking spears emerge from people's chests that reveal where they are going to go. He follows on his own which leads him to his parents room where he discovers his father's pistol, which will be of later significance. He discusses these with Prof. Monnitoff, indirectly, and asks if they would be a way to see into the future, like a form of time travel. Prof. Monnitoff explains that seeing your own path would give you the option to betray it, destroying all preformed destiny, which Donnie counters by saying that if "you travel in God's channel" this paradox would not occur. Although they are forced to conclude the conversation there, as faith is a topic which Prof. Monnitof cannot safely express his views as he is a teacher, Donnie reveals that he is using a spiritual basis to explain what he's experiencing.
The book Donnie receives from Prof. Monnitoff explains a lot of the strange phenomena that Donnie is experiencing. It explains the concept of a tangent universe exactly like Donnie is experiences. One part is the "Manipulated Living," which are the people around Donnie. It explains that all their actions are guiding the "reciever" (Donnie) to save the universe. How they do this sub-consciously, however is not explained in the book;
"There is a driving force behind the Manipulated's behavior... although we never find out what it is for sure. God is one of the most popular ideas mooted, the film does use religion at many points. The story uses lots of religious symbols and often points to the idea that you follow God's channel to decide your own fate." (Smith)
Part of coming of age is the struggle of finding, losing, or keeping our faith. Some will have doubts and experience something personal to each individual that cements and reaffirms their faith, or even causes them to align with another creed or something different entirely. Others will grow up and leave the thought confines of their family upbringing, without losing their faith. Still others will lose their faith, if they ever had it, and is often from an experience just as personal as those who retain it. No matter what happens to one's faith, there's a period following one's youth where he or she will be faced with alternatives to how they were raised and have the opportunity to change or retain their beliefs which is an important step to coming of age.