The Qur'an shows man the way to a realization of his goal on earth; it describes this path in the most complete terms. It is a way of correctly viewing the reality of things; a vision - personal, social and cosmic- based on a correct manner of behaviour and a precise method of interaction between men. In XLVI:30 we read that the Qur'an "guides to the truth and a right road, " meaning the road of right belief and correct action. On another occasion, mentioning the Torah and the New Testament, God says:
"We have revealed this Book to you with the Truth, confirming whatever Book was before it, and We keep watch over it" (V:48).
The Qur'an thus affirms the truth of the ways of guidance taught by the earlier prophets. In chapter XLII:13,
"He has ordained for you that religion which He commended to Noah and that which We reveal to you (Muhammad) and that We commended to Abraham, Moses and Jesus," and in chapter XVI:89, And We revealed the book to you as an exposition of all things."
Thus we understand from these verses that the Qur'an not only encompasses the meanings and teachings of all divine books revealed before it, but also adds to and completes them. Every thing which a man needs, both in terms of his spiritual and his social life, is contained and explained in the Qur'an.
source : http://www.maaref-foundation.com
