The song "Imagine" by John Lennon is about imagining something that could happen. This man is singing about a world of imagination where everything if perfect and nothing is wrong. No wars, no hunger, no violence, everything is perfectly perfect. All the people there would be living together and everything would be fine and alright.
This is like The Giver. In The Giver, everyone is living together and everyone is getting along perfectly. There are no wars, no hunger, no violence, everyone has what everyone else has. Everything there is perfect. In The Giver, everyone gets a job at the age of twelve, everyone has something to do, no complaints. Everyone gets a home and plenty of food. Everything is perfect and it is like a world of imagination.