A stenographer would have been needed to take down everything John has Jesus say in his farewell address to his disciples, chapters 14-17. As Matthew does in the Sermon on the Mount, John has gathered in these chapters, not only what Jesus said at the Last Supper, but also teachings from other times in his life. Jesus seems suspended between heaven and earth, which gives the sermon a timeless character.
He starts with what has become a famous line, "In my Father's house there are many mansions." He tells his disciples that he is going to the eternal world to prepare a place for them and will come back to take them there with him. This promise takes the edge off his departure and has been a comfort to Christians down through the ages whose loved ones have passed to the other world.