This movie is actually not about reincarnation. The theme of reincarnation consists the outer layer of the story. It does not make any difference if you believe in reincarnation or not to understand and appreciate what happened and why it happened in the movie. Love as the core fundamental need which binds all humans together is the main theme of story. A ten-year old boy finds some love letters from a woman madly in love with her dead husband. He 'wishes' to be the object of that love. This desire is so strong that the viewer wonders what has been happening in this boy's life that has created such a huge gap in his emotional make-up. His family is not wealthy. The father is a tutor and the mother is probably a homemaker. Maybe he is being neglected often. His family life is not explored sufficiently and it really does not matter. The viewer can construct various scenarios for his need to be loved the way that dead husband was loved by his wife.
Nicole Kidman, as a woman still in love with her dead husband, is torn between settling down with a man (her fiancée) who is 'able' to satisfy 'her needs' and her longing for a love which could fill her up to the brim with ecstasy and rapture. She is even willing to wait another eleven years for the young boy to become twenty one, so that they can marry. Although at the end of the movie, it becomes apparent that her love for her dead husband was not enough to keep him happy and content, it is a love capable of transforming a little boy to the degree of washing him off of selfishness and dishonesty (if there was any).
Going back to reincarnation theme, after looking at the movie from a psychological perspective, a firm believer in reincarnation could attest that the young boy was the dead husband understanding the value and depth of his wife's love only after his death. This view is plausible not because of the concept of reincarnation, rather for his inability to remember that he was dishonest to his wife and betrayed her.
The way this movie has been advertised and a couple of scenes which could make some viewers uncomfortable does not do justice to the profound message that the makers of the movie wished to bring across. This is not a movie for an average person. Do not expect to be swept off your feet with reincarnation philosophy or a love story. It is a painful, realistic, and utterly agonizing look at human beings struggling for a feeling, a force, or a fate which could define their lives.