The Qur'an constitutes the most comprehensive concept of Islam on the practical level as the source of the shari'ah, or the Divine laws and legislation. It is comprehensive because it includes law, as well as the underlying purposes and moral principles, and the creed to which every Muslim must subscribe. Islamic shari'ah is designed and suitable not only for Muslims, but for all mankind at all times. The Islamic law governs all human acts, by delineating every person's public or private-duties toward Allah and toward His Creation, including man.
Man-made laws are subject to alteration and are based on theories. Whenever a new body of legislators assumes authority, or a new theory appears and appeals to the legislators, the laws are changed accordingly. The Divine law, on the other hand, is unalterable and perpetual because the One Who made it is The Ever-living and Everlasting. He is the Creator Who created mankind and ordained for all human beings what is best for them until the end of time. For this reason, the Qur'an, being the last revelation to the last of the Prophets and Messengers, supersedes all previous Scriptures.