Pain’s popularity among Naruto fans can’t be overstated. The Rinnegan-wielding leader of the Akatsuki took command of every scene he was featured in through his intimidating presence and waxing philosophical about his one true path to Peace. He may not have been the series’ biggest fish but Nagato Uzumaki played an important role no other Naruto villain could, and in so doing brought one of the story’s most heartbreaking parallels full circle.
In search of power that would enable him to make his dreams of revenge a reality, Sasuke Uchiha fled the Leaf Village with the Sound Ninja 4 to join Orochimaru’s side. Naruto, along with the other Konoha Genin -- Shikamaru, Kiba, Choji and Neji -- set off in hot pursuit, believing Sasuke to be kidnapped. When they caught up with his group, the other genin took care of the Sound ninja, leaving Naruto to capture Sasuke. Shockingly, Naruto’s rescue mission transformed into a death match and as they exchanged blows, Sasuke highlighted an important difference between them.
As the two fought, Naruto had been trying to convince Sasuke to return to the Leaf Village. He compared Sasuke’s situation to his own, reminding his old friend that they were both orphans and could somewhat relate to each other. Rather than being comforted, Sasuke scorned Naruto and claimed the two were nothing alike. He described his pain as more intense than Naruto’s since he’d actually gotten to experience love from his family and clan members. Naruto had always been alone, and Sasuke believed that he was much worse off since he’d previously had love and then lost it in such a cruel way.
As insensitive as Sasuke’s statement was, there was some truth to it. Before joining Team 7, Naruto had very few friends in the Leaf Village. Those he’d managed to make -- including Sasuke himself and Sakura -- had never been taken from him in one way or another. He couldn't fully understand the hatred toward Itachi that Sasuke carried in his heart, and as such had no moral authority to ask Sasuke to give up on his revenge. The duo just couldn’t see eye to eye on this particular issue -- until Jiraiya’s death.
Naruto was understandably heartbroken at his master’s death by Pain’s hands. Jiraiya had been the closest thing to a father figure Naruto had, and he swore to pay Pain back in kind. Their battle in Konoha’s ruins was legendary and Naruto came out on top; but after hearing Pain explain the cycle of hatred, he couldn’t bring himself to end his master’s killer. He chose instead to break the cycle by sparing Pain’s life and rose above the revenge he desperately sought -- just like he'd advised Sasuke to do years ago.
This aspect of Naruto and Sasuke’s relationship perfectly illustrated Pain’s notion of never being able to understand another human until one had experienced the hurt they did. For the first time, Naruto realized just how Sasuke must have felt after losing his family.
Choosing to spare Nagato in the end honored the words Naruto had carelessly spouted at Sasuke when they were kids. When he repeated them to Sasuke during their final fight, his gospel of forgiveness wasn’t just empty advice given by an immature child desperately trying not to lose his best friend. They were words of wisdom shared by a partner in suffering who understood the enormity of what he was asking, and that it would be the only way to quell Sasuke’s inner turmoil.
