At the end of the war when Hagoromo(sage of six paths) is about to dispell the edo tensei, he sees how much it hurts naruto his own sons reincarnation to say goodbye to his father. So he decides to take Pity on naruto by reviving Minato completely. But back at the village Hagoromo has Another present ready

In a botched sealing Minato accidentally allows Naruto to speak with all of his dead ancestors and the greatest men of their time via his Mindscape as an unspoken deal with the Shinigami.