7 Lastly, the duty of religiously defending the truths divinely delivered, and of resisting those who dare oppose them, pertains to philosophic pursuits. Wherefore, it is the glory of philosophy to be esteemed as the bulwark of faith and the strong defense of religion. As Clement of Alexandria testifies, the doctrine of the Saviour is indeed perfect in itself and wanteth naught, since it is the power and wisdom of God. And the assistance of the Greek philosophy maketh not the truth more powerful; but, inasmuch as it weakens the contrary arguments of the sophists and repels the veiled attacks against the truth, it has been fitly called the hedge and fence of the vine.(22) For, as the enemies of the Catholic name, when about to attack religion, are in the habit of borrowing their weapons from the arguments of philosophers, so the defenders of sacred science draw many arguments from the store of philosophy which may serve to uphold revealed dogmas. Nor is the triumph of the Christian faith a small one in using human reason to repel powerfully and speedily the attacks of its adversaries by the hostile arms which human reason itself supplied. This species of religious strife St. Jerome, writing to Magnus, notices as having been adopted by the Apostle of the Gentiles himself; Paul, the leader of the Christian army and the invincible orator, battling for the cause of Christ, skillfully turns even a chance inscription into an argument for the faith; for he had learned from the true David to wrest the sword from the hands of the enemy and to cut off the head of the boastful Goliath with his own weapon.(23) Moreover, the Church herself not only urges, but even commands, Christian teachers to seek help from philosophy. For, the fifth Lateran Council, after it had decided that "every assertion contrary to the truth of revealed faith is altogether false, for the reason that it contradicts, however slightly, the truth,"(24) advises teachers of philosophy to pay close attention to the exposition of fallacious arguments; since, as Augustine testifies, "if reason is turned against the authority of sacred Scripture, no matter how specious it may seem, it errs in the likeness of truth; for true it cannot be."(25)
Source: Aeterni Patris (Vatican.va)