Father and Son Relationship
The central theme of the movie is the father-son relationship. Will and his father are estranged because Will feels that Edward's tall tales have become too extreme and have pushed them apart. Edward's storytelling, the fact that it is both so attention-grabbing and seemingly fantastical, frustrates Will because he wants to know the truth. After years of believing in the fairy tale version, Will wants his father to tell it like it is, but reality is not quite in Edward's vocabulary, and he prefers the mythic. Thus, the tension between them, the fact that Will wants Edward to be a different kind of person, creates an unbridgeable rift.
When Edward is sick with cancer and goes off chemotherapy, Will returns home in hopes of repairing their relationship. In doing so, he finds that he actually begins to understand his father in a way that transforms their relationship and makes him appreciate the uniqueness of Edward's nature. Ultimately Will realizes that his father's way of seeing things differently is his way of wanting to feel more connected to others. Will is able to finally differentiate from his father and realizes that their differences are not as bad as he had thought.
Fantasy vs. Reality
Another major theme in the film is the boundary and tension between fantasy and reality. While Will wants to hear the actual account of things, Edward is convinced that there is magic in the world, and his stories reflect his magical thinking. In his eyes, anything is possible; giants, witches, and werewolves roam among us, and time literally stops when one falls in love. Throughout the film, Will tries to get his father to admit that he is making things up, that there is a logical explanation for how he remembers events, but Edward insists upon his version, and tries to instill in his son that the more fantastical version can reflect a greater reality than the literal facts ever could. By virtue of his enduring belief in the power of magic, Edward gets Will and those around him to believe more in a philosophy of life that is more spiritual and everlasting, and a deeper connection and presence with the world around them.
Love
In spite of his stretching the truth, and all their years of marriage, Edward and Sandra remain deeply in love into old age. Sandra looks admiringly at her husband, and fears being left behind by his death. While Will suspects that his dad must have cheated on his mother at some point, we learn that he has been faithful the whole time, and we see their love reflected in little moments of devotion. When Edward first meets Sandra, he is struck by her beauty, and works for three years without pay just to learn her name. When he learns where she goes to school, he plants her favorite flower, daffodils, outside her bedroom window, and seeks to show her how steadfastly devoted he is to her. The two of them have a fairytale romance, reflected by their loyalty and respect for one another. Love, and the magical power of love, is a major theme of the film.
Death
For all its sunniness and magic, the film also deals a great deal with the theme of death. From an early age, Edward is unafraid of his death, and looks bravely into the witch's prophetic eye to see the premonition of his death. From that day forward, he lives bravely because he knows that death is not coming for him yet. By the end, Edward has terminal cancer and is approaching the end, but he maintains his fighting spirit. In anticipation of Edward's death, Will must grapple with his alienation from his father, and find ways to connect with him before he loses him. By the end, Will learns, with the help of his father's mythical sensibilities, that death does not need to be a definitive and terrifying fate, but another adventure. When Edward asks Will to tell him the story of his death, Will concocts a mystical explanation, that Edward will turn into a fish and swim in the river forever. Through storytelling, Will learns that people can outlive their bodies, and the myths we tell each other can help us to process the inevitability of death and change.
Bravery
Because Edward is so acquainted with the concept of death, and feels so sure that his death will not occur until he is older, he is blessed with an unfailing bravery and sense of optimism. Even in the most difficult of trials, he holds fast to his belief that it is not his time yet, and so pushes through situations that others would be far more frightened of. He has a plucky optimism that things will be alright, even when faced with a dark and menacing forest, a hungry giant, broken bones while working at the circus, a risky war maneuver, and the teeth of an angry wolf. Edward is defined by his bravery and fortitude.
Ambition
In Edward's childhood, he suddenly begins growing very quickly, and he has to get hooked up to a machine while his bones outpace the rest of his body. Ever the whimsical mind, young Edward does not just interpret this development as a side effect of the inevitability of puberty, but as a symbolic growing as well. He draws a comparison between himself and a goldfish that will not grow if it stays in a small bowl, and interprets his growth spurt as evidence that he is destined for bigger things than his small town can offer. An important element of Edward's story is that he has big dreams of an important and adventurous life, that he is ambitious beyond what his "small pond" has to offer.
Loneliness & Acceptance
When he is confronted with the wolf living in Amos' trailer (which is really just Amos in werewolf form), Edward is frightened, but not driven to hurt the wolf. Instead, he finds a way to make friends with the wolf by throwing a stick for it to catch. In this moment, he narrates, "It was that night I discovered that most things you consider evil or wicked are simply lonely, and lacking in the social niceties." This is at the heart of Edward's goodness and his belief in everyone's goodness. In his eyes, when people or entities seem like they are evil or out to get you, it often has to do with an internal darkness with which the person or entity is struggling to reconcile, or a sense of loneliness. Edward believes that in order to help other people, one must help them to alleviate their loneliness by showing them acceptance.