Created by Hagoromo Otsutsuki as a means of maintaining peace within the Uchiha clan and the larger shinobi world they inhabited, the Uchiha stone tablet was a sacred monument concealed within the Naka shrine in Konohagakure. Hidden in the clan's secret meeting room, located beneath the seventh tatami mat on the far right of the space, the tablet was considered an integral part of the Uchiha's heritage, with its contents said to be a record of the shinobi world's history. Throughout the story of Naruto, it was repeatedly stated that the tablet could only be read with specific dojutsu. While the Sharingan and its evolved form, the Mangekyo Sharingan could decipher parts of text, the entirety of the tablet could only be read by those in possession of the Rinnegan. Considering the value placed on its contents as well as the clandestine nature of its existence, the tablet naturally played a massive role in Naruto, having been the source of Madara's Eye of the Moon Plan.
Until his betrayal by Black Zetsu, Madara firmly believed that triggering the Infinite Tsukuyomi, as stated by the tablet, would be the path to a lasting peace in the shinobi world. His possession of the Rinnegan and Eternal Mangekyo Sharingan also made him one of the few capable of interpreting the tablet's contents in their entirety. It is this very aspect of the narrative that fails when called into question, as the reveal of Black Zetsu having altered the tablet's contents seemed to come out of the blue. There was little to no foreshadowing about this aspect of Naruto's storyline, which played a considerable role in the introduction of the story's final antagonist, Kaguya Otsutsuki. Hence, this plot point regarding the revision of the tablet's contents was almost like a convenient retcon which allowed Madara to make way for her.
The History Of The Stone Tablet
Once Hagoromo created the tablet and passed on his knowledge of Ninshu to his many followers, the artifact fell into the hands of the Uchiha clan, who were the descendants of his son, Indra Otsutsuki. Driven by the Curse of Hatred, which was kept alive by Indra's reincarnations over the centuries, the Uchiha became one of the most powerful clans which were active during the Warring States period, with the Senju clan being the only ones capable of competing with them, by virtue of being the descendants of his brother, Asura Otsutsuki. Armed with the power of the Sharingan, and led by the few who managed to awaken the Mangekyo Sharingan, the Uchiha safeguarded the stone tablet as a hallowed piece of their history, and were among the few capable of reading its text. This was fairly in line with Hagoromo's initial intent of having the tablet serve as a deterrent against Kaguya's revival, warning those in the future about the dangers of the Infinite Tsukuyomi and the God Tree.
Inscribed on its surface were the secrets of the Mangekyo Sharingan such as the process behind obtaining it as well as its use in controlling tailed beasts, the history of Kaguya, the God Tree, and the Sage of Six Paths, along with warnings about the Infinite Tsukuyomi, some of the clan's secrets, and details about Madara Uchiha's body. Initially, these bits of information were the only established parts of the text that had been deciphered, even when most of the Uchiha did not have the Rinnegan's abilities required to decipher and comprehend the entirety of the tablet's contents. However, in Madara's final moments, Black Zetsu revealed that he had added another line about the Infinite Tsukuyomi being the only avenue for the Uchiha's salvation, a statement that Madara took to heart.
Madara's Eye Of The Moon Plan
Madara Uchiha, the head of the clan during the Warring States Period and perhaps its strongest ever member, was able to read the inscriptions on the tablet after founding Konohagakure with the future First Hokage Hashirama Senju, his childhood friend. He took note of the Infinite Tsukuyomi, but at first, still believed the shinobi world could find peace through diplomacy over time. Once Hashirama and Madara fell out over the course of the village's development, leading to their fated battle at the Valley of the End, the latter faked his death and resolved to embark upon a lifelong campaign to set the plan in motion and see it out till its conclusion. Firstly, he used Hashirama's DNA to awaken the Rinnegan, by mixing the chakra of Asura and Indra. Following his death, he passed on his mission to Obito, who manipulated the Akatsuki while posing as Madara himself. This transformed the once peaceful organization into a haven for extremely powerful rogue ninja, employed to collect all nine tailed beasts for the purpose of reviving the Ten-Tails.
Aiming to end all conflict by imprisoning all life on earth in a never-ending genjutsu, Madara believed that his solution was benevolent. Unfortunately, he was unaware that this would bind them all to the God Tree and harvest their energy for the purpose of creating a chakra fruit. He was also impeded from his goal after being brought back by the Summoning: Impure World Reincarnation jutsu throigh intervention of Obito, who absorbed the Ten-Tails to become its first jinchuriki. In the end, Madara managed to fully reincarnate himself into the world, fulfilling the need for him t become a living vessel for the Ten-Tails, allowing him to absorb its power into himself and commence the Infinite Tsukuyomi. He did so by flying up into the atmosphere and reflecting the image of his own Rinne Sharingan onto the moon.
The Convenience Of Kaguya's Revival
For most, it might have appeared as if Madara had emerged as the final victor, as the majority of the world was now trapped within the Infinite Tsukuyomi, even when Sasuke and Naruto had gained incredible new powers. After announcing himself as the world's savior and the only living combatant left standing apart from Team 7 and Obito, Madara flew back to finish the rest of them off, only to have Black Zetsu stab him in the back, force-feed him the chakra from the God Tree, and finally, force him to transform into a revived Kaguya. While this took place, Zetsu also revealed that he was not an embodiment of Madara's will, but rather, of Kaguya's, sharing that he was the one responsible for rewriting the text about the Infinite Tsukuyomi.
This sudden change of course effectively erased any hope of a final confrontation with Madara, who had been steadily built up as the series' main antagonist for hundreds of chapters at this point. Additionally, there were several inconsistencies regarding the rewritten text on the tablet which guided Madara to execute the Eye of the Moon Plan. For starters, Black Zetsu should not have been able to read let alone rewrite the tablet's text as it possessed neither the Mangekyo Sharingan nor the Rinnegan. Secondly, it is nigh on impossible that Madara, one of the strongest and most intelligent shinobi in history, and perhaps the greatest Sharingan user until Sasuke, did not notice that the tablet had been tampered with. Finally, the idea that Madara as the Ten-Tails jinchuriki, could simply transform into Kaguya with the Ten-Tails chakra also seemed exceedingly convenient, highlighting how this aspect of the plot seemed to be an alteration that was not as well fleshed out as earlier parts of Naruto. This also sidelined Madara, who was a much more compelling antagonist than Kaguya, sparking off the never-ending debate regarding Naruto's conclusion, which all traces back to the revision of the stone tablet.