I think he gave Naruto a genjutsu counter. So that the "eyes that control the nine-tails" will be ineffective and Naruto can use the kyuubi's chakra to the best of his abilities.
what if it wasnt power but it was the real truth behind all of itachis plans and the truth about madara and the elders .maybe a genijutsu that lets you see what itachi wanted susake to see what the elders said what madara did . i think of it like this b/c if itachi gave it to naruto then susake must believe it and no one would be expecting for this kind of outcome instead of power thats what we all believe it was a genijutsu that susake will see. a big twist???
After uchiha massacre , everyone in academy knew about it. Naruto was going with Sasuke to the same class so how could he dont know Itachi ? Everyone in konoha knew him like a genius so how naruto could didnt know him ? How Naruto couldnt know about massacra ? Naruto never say that he know all about it , only after that day when Sasuke told him about it. Your thoughts ?