In Manichaeism the “three worlds” are also referred to as the “three ages” or “three eras.”
In the beginning the Spiritual World of Light and the Material World of Darkness were separate.
Disciples of Mani believe humanity currently exists in the Second Age which is characterized by the mixing of Light and Darkness. Manichaeans believe Light has been trapped in a physical body which was designed by the forces of the World of Darkness. According to divine revelatory texts, it is during the latter part of the Second Age that a Messenger will appear in the world of mankind to help bring a message of hope to the world. Manichaeans believe that his teaching will help individuals realise their true origin and liberate the Light within from the darkness.
The Third Age is future. The Church teaches that this age will bring about the division of Light and Darkness once again. The Light that is trapped in the physical body will be separated and return to God in the Celestial Kingdom of Light.