Reading my own interpretation into the film, the first thought that came to my mind while watching it was that a subtitle for the movie could have been "Cain Verses Abel". However, the further we got into the movie, I think a better subtitle could have been "Jacob Verses Esau".
The reason for this subtitle is based on the observation that a particular conversation comes up at least twice. The second time it comes up, it does so in a context when the boys, who were stranded on an Island without adult supervision, become divided under the leadership of polar opposites.
The First Leader, who is more like Jacob/Abel, believes that, although, they may never be rescued, they ought to live in such a way as to be prepared in the case help does arrive. The Second Leader, Cain/Esau, decides that help is never coming and even if it does, it is irrelevant to his plans.
What is interesting is that the Second Leader denies the future possibility of a rescue while ignoring the evidence that the military is indeed looking for them when a helicopter flies by. Due to his hunting ability, he determines to survive on his own and allows the "signal fire" to die out. Thus missing not only the opportunity to be rescued, but purposely orders his followers to do the same.
The part that reminds me of an incident between Jacob and Esau is when everyone, except "Piggy" abandons the First Leader for the hunter. Meat is offered to the starving boys, but Ralph, the First Leader, rejects the offer. For if he accepts the offer, he would become a slave to the wickedness of the Second Leader.
At the end of the movie, the Hunter and his followers become totally depraved and seek to murder Ralph. Ralph runs for his life and the movie comes to a climax when Ralph makes it to the beach and lands at the feet of a soldier, who asks, "What are you doing?"
I do not know if the author of the book or the director of the movie are Christians. But this idea is exactly what the Bible teaches. Men suppress the truth of a coming day of final judgment. We ignore all of the signs around us. We seek to live for this age and the present. Yet by God's grace, He has called some men unto Himself. He has caused within the hearts of men to not seek after that which is perishing, but instead to seek that which is eternal.
There is a day coming when the wicked will be seen for what they are. They will pursue the righteous in wickedness. Yet in that Day, Christ will appear. He will ask, "What are you doing?" He will judge the thoughts and intentions and deeds of men. It is to this Blessed Hope that the Christian must constantly be reminded to turn his eyes.
Psa 10:2 In pride the wicked hotly pursue the afflicted; Let them be caught in the plots which they have devised.
Psa 1:6 For the LORD knows the way of the righteous, But the way of the wicked will perish.