On the necessity of studying ancient philosophy
If someone today wished to grasp on his own all of the proofs inferred by those in the legal schools who reflect upon the controversial questions debated in most Islamic countries, even excepting the Maghrib, he would deserve to be laughed at, because that would be impossible for him--in addition to having already been done. This is a self-evident matter, not only with respect to the scientific arts, but also with respect to the practical ones. For there is not an art among them that a single person can bring about on his own. So how can this be done with the art of arts--namely, wisdom?
Since this is so, if we find that our predecessors in former nations have reflected upon existing things and considered them according to what is required by the conditions of demonstration, it is perhaps obligatory on us to reflect upon what they say about that and upon what they establish in their books. Thus, we will accept, rejoice in, and thank them for whatever agrees with the truth: and we will be alert to, warn against, and excuse them for whatever does not agree with the truth.
From this it has become evident that reflection upon the books of the Ancients is not only obligatory according to the Law [Sharia], for their aim and intention in their books is the very intention to which the Law urges us. And it has become evident that whoever forbids reflection upon them by anyone suited to reflect upon them--namely, anyone who unites two qualities, the first being innate intelligence and the second Law-based justice and moral virtue--surely bars people from the door through which the Law calls them to cognizance of God--namely, the door of reflection leading them to true cognizance of Him. This is extreme ignorance and estrangement from God.
Averroes [Ibn Rushd], The Decisive Treatise, trans. Charles E. Butterworth (Brigham Young Univ. Press, 2001), § 8-10.