The main theme of the song "Imagine," written by John Lennon, revolves around the concept of peace and unity among humanity. In the lyrics, Lennon encourages listeners to envision a world without divisions caused by religion, national boundaries, or material possessions, promoting an ideal of global harmony. The song conveys a hopeful message that such a world is achievable if people work together towards understanding and love. Its powerful and simple message has resonated with audiences since its release in 1971, making "Imagine" an anthem for peace movements and a lasting expression of idealism.