The concept of a game is the novel's major theme. All of the other important ideas in the novel are interpreted through the context of the games. Ender wins all of the games, but it is not so clear what that means. He thinks for a large part of the book that the games are no more than they appear, and he does not realize the real meaning of his final game until it is far too late. The difference between what is a game and what is reality becomes less and less clear as the story unfolds. The very first game played in the book is "buggers and astronauts," a game that Peter makes Ender play, and it is a game that all kids play. However, in Ender's case the game is more than it seems, because Peter's hatred for him is real, and he inflicts physical pain upon Ender in the course of the game. This is one game that Ender never wins.
At Battle School, Ender faces two different types of games. On his computer he plays the mind game, a game that even its creators do not properly understand and one that effects Ender's life in direct ways. It is through the mind game that Ender is able to come to terms with the changes that are occurring in his life and it is the images of this game that the buggers use to communicate with Ender at the end of the book. In the battle room Ender plays war games. These games are everything to the kids at the school. Their lives revolve around playing games, and so the meaning of the word itself shifts from a voluntary fun experience to a necessary and crucial aspect of life. These games and their implications cause Bonzo's death and create rancor and jealousy throughout the school.
Finally we come to the greatest games that Ender plays, while he is the commander of the Third Invasion. Playing these games is debilitating to Ender's health. He cannot sleep, he barely eats, and he is forced to be a leader and not a friend to those whom he cares for. Ender destroys the buggers because he wants the games to end, and he is successful, but if he had ever known that it was not a game he never would have participated. In the end it is not very clear how to separate a game from reality, for the playing of a game can have a profound impact on a life, and sometimes the game itself is reality.
Much of Ender's Game details the lives of children, and at every point they are contrasted with those of the adults around them. Although the adults often manipulate or control the children, this is not always the case. Peter and Valentine, two kids, manage to dominate the worldwide political system through their control of adults. Ender, who does not wish do exert influence over anyone, is brutally manipulated by adults, yet even they are aware of his superior intelligence. Children in this book are smaller than adults in size, but that is about the only difference. Their thoughts are just as real, and their emotions just as valid as their older counterparts. In fact, even the International Fleet commanders who use them are aware of this, because they are willing to place the fate of humanity in Ender's hands. Children must be taken seriously, for they are capable not only of killing, manipulating, and hating—the worst features of adults—but also of creating and helping.
Compassion is the redeeming feature in Ender's Game. Compassion is the theme that runs through Ender's life. It is the defining feature of his existence. The reason that he plays the games so well is his ability to understand the enemy and to inspire loyalty. More than that, it is compassion that saves Ender. If not for his compassion he would have been turned into an automaton; he would have become either a killing machine or a power hungry creature like Peter. Ender's compassion for the buggers makes possible for him to make up for destroying their race by giving them a chance to start anew. Graff's compassion for Ender causes him to seek Valentine's help, and her compassion in part is what saves Ender when he despairs. Even those characters who are not allowed to show their compassion, like Mazer Rackham, later demonstrate that they are capable of it, and it makes them human. Finally, the buggers demonstrate compassion to Ender, and this convinces him that he must make it his mission to see that their queen is found a safe home to start anew. Compassion provides hope for the future.
This is the dangerous theme of the book, the one that, if not overcome by compassion, will lead to the destruction of humanity. Ruthlessness is sometimes necessary, as in Ender's treatment of Stilson, but it is a last resort, something to be avoided at all costs. Colonel Graff, Major Anderson, and Mazer Rackham are forced to be ruthless in their treatment of Ender, but they do so in order to save humanity, and they have compassion for the boy even as they act. Only Peter is purely ruthless, and in him the danger of pure manipulation without conscience comes into full effect. Peter is able to gain what he wants because he does not care about others, and he will stop at nothing. Ruthlessness is the human condition devoid of its humanity, and it is the danger that threatens total destruction.
In Ender's Game it is never entirely clear who is a friend and who is an enemy. Graff, Anderson, and Rackham, who are undoubtedly Ender's friends, appear to him as enemies and are forced to do so. Peter attempts to befriend Valentine merely to get what he wants, but she never forgets that he is not a real friend. Petra Arkanian and Dink Meeker are always Ender's friends, but at times he is uncertain of where they stand. But by far the most striking juxtaposition occurs with the buggers. The only enemy that Ender truly fears, the buggers in the end prove to be friendly. The earth's greatest enemy, the alien race it was at war with, turns out not to have been intentionally hostile. Card constantly proves that friends and enemies are not clear distinctions.
The question of what it means to be human is taken up several times in Ender's Game. In the first place, children are affirmed to be just as real human beings as adults, even as the children are robbed of their youth. It is, after all, a group of children who save the world. But more fundamentally than this, to be human is to have compassion. The ability to feel for others is the mark of humanity. Peter's humanity is questioned, while Ender's is what saves the planet. In the end, the buggers themselves suggest to Ender that if things had gone differently both races could have celebrated the other's humanity. Their compassion for the humans they killed and their sorrow over the war means that they are human, and this is why Ender feels the need to do something to help them and why he so keenly mourns his destruction of their race.
Ender is very much a representative of all that is good. He is filled with sorrow for any destruction he causes and wishes no ill to any other creature. He is good because he is kind, but he is also good because he makes the sacrifices that he has to make. It is good to do what is needed, even if what is needed does not seem right. Ender does not hate Graff or Rackham for what they did to him, because he realizes that they did what had to be done. At the same time, he is crushed by the thought that he wiped out an entire race. He is good because he is forgiving—he understands even those who hate him. Finally, Ender is good because he sees his evils and tries to remedy them. There is no idealized, perfect good in this novel. Ender represents the best that a person can do, given the circumstances of life.
Peter does what he wants. He takes power because he desires it, and other people's thoughts and emotions are only important to him insofar as he can exploit them. It is true that he makes a good ruler because he is not evil incarnate. Evil in this book is acting for the wrong reasons, regardless of the outcome. Although Peter saves lives by coming to power on earth, he is evil because he did so only out of expediency. Good can come out of evil, but that does not make the evil any better. Peter is an awful human being, but it just so happens that he makes a good ruler. What is scary is that an evil person does not care whether their actions are good or bad.