We could raise a legitimate question here if we say that the God who revealed his truth in Koran is the same God who also revealed in the Old testament and the one who sent Jesus Christ. Why would he reveal another message through Mohammed if Jesus was the ultimate sacrifice and the fulfillment of the old testament prophecies about the messiah? Isn't the cross of Christ enough to save humanity? aren't the message of the old testament prophets enough? How about the teachings of Mormonism who also claims that God revealed his truth to Joseph Smith?
YouTube - Three tests to discuss truth - Dr. Ravi Zacharias
It would only cause confusion to the world.