In 1544, in "De orbis terrae concordia", ("Concerning the Harmony of the Earth"), Postel advocated a universalist world religion. The thesis of the book was that all Jews, Muslims and heathens could be converted to the Christian religion once all of the religions of the world were shown to have common foundations and that Christianity best represented these foundations. He believed these foundations to be the love of God, the praising of God, the love of Mankind, and the helping of Mankind.