The main theme of the film, of course, is the "pay it forward" (as opposed to "pay it back") idea. A character receives a substantial favor from another, but is not allowed to pay it back. Rather, he or she is to do deeds on behalf of three others, who are to respond likewise. While the particular formulation in this film (the power-of-three mathematics) may well be original, the concept of unconditional love is not a new one by any means. It is deeply rooted in the Bible, and this film can well be a good starting point for any discussion of agape in the church.
Many who have seen the movie have complained about the ending, which is often described as hopelessly maudlin. All I can say to those critics is that they somehow missed something very important. The key to this piece of fiction is that Trevor’s "pay it forward" had a success far greater than anyone had realized. And the choice of music that accompanies the closing scene, "Calling All Angels," is the film's only explicitly "religious" element. Only in its tragic conclusion, deliberately done with no dialog to subtract from the images on the screen, can the full fulfillment of that payoff be portrayed. So grab a box of Kleenex and watch this film. You will be blessed.