Philosophy is worthy to assume the sacred wisdom
Opus Majus, Pars II
Hence it follows of necessity that we Christians ought to employ philosophy in divine things, and in matters pertaining to philosophy to assume many things belonging to theology, so that it is apparent that there is one wisdom shining in both. The necessity of this I wish to establish not only on account of the unity of wisdom, but because of the fact that we must revert below to the lofty expressions relating to faith and theology, which we find in the books of the philosophers and in the parts of philosophy: so that it is not strange that in philosophy I should touch upon the most sacred truths, since God has given to the philosophers many truths of his wisdom.
The power of philosophy must be applied to sacred truth as far as we are able, for the excellence of philosophy does not otherwise shine forth, since philosophy considered by itself is of no utility. The unbelieving philosophers have been condemned, and "they knew God, and did not glorify Him as God, and therefore became fools and perished in their own thoughts," and therefore philosophy can have no worth except in so far as the wisdom of God required it. For all that is left is in error and worthless; and for this reason Alpharabius [that is, al Farabi, the Islamic natural philosopher] says in his book on Sciences that an untaught child holds the same position with respect to a very wise man in philosophy as such a man does toward the revelation of God's wisdom. Wherefore philosophy by itself is nothing, but it then receives vigor and dignity when it is worthy to assume the sacred wisdom. Moreover, the study of wisdom can always continue in this life to increase, because nothing is perfect in human discoveries. Therefore we of a later age should supply what the ancients lacked, because we have entered into their labors, by which, unless we are dolts, we can be aroused to better things, since it is most wretched to be always using old discoveries and never be on the track of new ones, as Boetius says, and as we proved clearly above in the proper place.
Christians likewise ought to handle all matters with a view to their own profession, which is the wisdom of God, and to complete the paths of the unbelieving philosophers, not only because we are of a later age and ought to add to their works, but that we may compel the wisdom of the philosophers to serve zealously our own. For this the unbelieving philosophers do, compelled by truth itself as far as it was granted them: for they refer all philosophy to the divine wisdom, as is clear from the books of Avicenna on Metaphysics and Morals, and from Alpharabius, Seneca, and Tullius [that is, Cicero], and Aristotle in the Metaphysics and Morals. For they refer all things to God, as an army to its chief, and draw conclusions regarding angels and many other things; since the principal articles of the faith are found in them; for as will be set forth in the morals, they teach that there is a God and that he is one in essence, of infinite power and goodness, triune in persons, Father, Son, and Holy Spirit, who created all things out of nothing; and they touch on many things concerning Jesus Christ and the Blessed Virgin. Likewise also they teach us of Antichrist and the angels and of their protection of men, and of the resurrection of the dead and of future judgment and of the life of future happiness promised by God to those obedient to him, and of the future misery which he purposes to inflict on those who do not keep his commandments. They write also innumerable statements in regard to the dignity of morals, the glory of laws, and concerning a legislator who must receive the law from God by revelation, who is to be a mediator of God and men and a vicar of God on earth, the Lord of the earthly world. When it shall be proved that he has received the law from God, he must be believed in all things to the exclusion of all doubt and hesitation; who must direct the whole race in the worship of God and in the laws of justice and peace, and in the practice of virtues because of the reverence of God and because of future felicity. [We must avail ourselves of their teachings] because they wrote that the worship of idols should be destroyed, and because they prophesied of the time of Christ.
From whatever source the philosophers got these statements and similar ones, we find them in their books, as a clear proof will show in what follows, and any one can discover the fact who cares to read through the books of the philosophers. For we cannot doubt that these things were written by them, from whatever source they received them. Nor should we be surprised that philosophers write such statements; for all the philosophers were subsequent to the patriarchs and prophets, as we brought out above in its proper place, and therefore they read the books of the prophets and patriarchs which are in the sacred text.
Opus Majus, translated by Robert Belle Burke (Philadelphia: University of Pennsylvania Press, 1928), vol. 1, pp. 65-67.