The importance of the Quran is best comprehended once we have established a good understanding of the purpose of this Holy Book. All the prophets that have been sent by God hold one reason as their objective and mission, that is, the guidance of mankind. With each prophet and apostle, the commands and instructions God has sent with the previous messenger would be completed, as were the books that were revealed to each prophet. Hence, the purpose of each Holy Book can be stated as such:

Verification and completion for the books that came before it
Guidance for humanity

Since God has intended to guide mankind, it is logical that He should send a book along with the religion in order for the people to seek commandment and guidance from it. From this we can understand the importance of the Quran better. The Quran which is the last Holy Scripture revealed to the last Prophet is both guide and verification as stated in the Book itself. The guidance of mankind would be redundant had God not sent a book in which all His rules and instructions have been existed. Subsequently, when a person sets foot unto the path of monotheism and seeks guidance, they would need a manual whose authenticity and endurance are reliable for reference.