Naruto has switched central themes more than once as it's serialization progressed. At first the story was a "quest story" about Naruto's growing up in a world of ninja, then it was "light versus dark" thing with him and Sasuke, then "defeating war"(
), and then it was back to a "light versus dark" but this time with Senju and the Uchiha. The result of all this has been a gordian knot of plot threads.
No, Naruto has largely been thematically consistent. Since the beginning Naruto has been about finding acceptance through understanding and compassion. This was presented as the central theme as early as the Zabuza arc. Presentation has largely been consistent: first Naruto is faced with a fellow outsider (Zabuza and Haku, Gara, Nagato, Sasuke, Tobi, Kabuto, Orochimaru). He shows them empathy, sympathizing with their plight. If an emotional breakthrough can be made, the fight ends with Naruto demonstrating the power of compassion. If a breakthrough is not possible, Naruto is always prepared to fight to defend his ninja way, defeating the forces of hatred in combat. With the strength of compassion and understanding, Naruto overcame the animosity of his fellow ninja's, becoming an outsider no longer, but an integral member of the community. Having overcome his outsider status in Part I, Naruto turned too a larger stage, hoping to bring compassion and understanding to the world at large. The War promised to fulfill his mission: all of the world's nations, once adversaries, have become allies against the forces of hatred. Tobi's defeat will be the ultimate symbol of the forces of compassion and understanding defeating hatred and vengeance.
Light vs. darkness is simply another way of saying compassion vs. hatred. At least in initial execution Kishi's intentions were far more nuanced than simply good vs. evil or light vs. darkness, at least trying aiming for something more human, tangible, and easier to relate too. While the execution has slipped over the years, compassion (will of fire) vs. anger (power of hate), has remained central to the plot.
A quest story is a genre, representing a series of plot conventions and a style of narrative progressions. Themes are the moral behind the story, the deeper message the author hopes to convey. One Piece is a classic example of a quest story: the hero leaves home on a long journey, hoping to find an object shrouded in mystery, possession of which would symbolically grant him the status of greatest hero of his age. One Piece is a perfect example of the hero's journey, similar to Jason and the Golden Fleece. Naruto could be construed as a quest of sorts, though in a less archetypical sense. Naruto is a quest of self discovery and acceptance, as the plucky outsider gains acceptance, respect, and ultimately the admiration of those who once rejected him. His goal of becoming Hokage could be seen as represented the ultimate acceptance, the outsider becoming political leader of the village. Actual attainment of the hokage's office is not necessary for completion of the quest. Defeating Tobi and becoming one of the greatest heroes of the ninja world would be more than enough to fulfill Naruto's quest. It would be enough to know that Naruto will be one of the next in line for Hokage, that when the time comes it is as good as his. Otherwise it is a simple matter of Tsunade dying a heroes death and the manga ending with Naruto being declared Hokage by acclaim. Calling Naruto a quest in the classic sense would be a massive stretch though, one could if they were inclined, and if so, it is as much a quest now as it was when the series began. AS with all quests, Naruto's journey must come to an end. By achieving the measure of acceptance defeating Tobi promises too bring, the central conflict of the series and main themes will be resolved. Any further exposition would be needless.
Naruto can wrap up any time precisely because all loose ends have been tied up. Most major plot line has been closed, those that are not will be closed with the defeat of the antagonists. It is important to remember that writers should never spell everything out for the audience. It is up to the reader to infer at least a part of the stories meaning. Nothing is worse than an over didactic writer, robbing the audience of the ability to think, interpret, and comprehend the implications of what has happened.
