Final answer:
The Qur'an is considered the authority for all Muslims on God, how God expects people to live, and the eternal destiny of humankind. It is believed to be the word of God as revealed to the Prophet Muhammad and contains instructions and guidance on various aspects of life.
Step-by-step explanation:
The messages in the Qur'an are considered the authority for all Muslims on God, how God expects people to live, and the eternal destiny of humankind because Muslims believe that the Qur'an is the word of God as revealed to the Prophet Muhammad through the angel Gabriel. The Qur'an contains instructions and guidance on various aspects of life, including moral and ethical teachings, social and legal principles, and guidance on worship and rituals. It is believed to be the final and most complete revelation from God, superseding all previous scriptures.