The main theme of the Quran is Tawheed or the Oneness of God. This means believing that Allah is the one and only God and all acts of worship should be directed to Him alone. The Quran discusses different aspects of Tawheed including the unity of Lordship, unity of Allah's names and attributes, and unity of worship. Shirk is the opposite of Tawheed and means associating partners with Allah in any form, such as worshipping other beings besides Allah. The document provides examples of different types of Shirk and emphasizes that true belief is to worship only Allah and seek his help alone.