In the four preceding books, my very dear friend, which I put forth to you, all the heretics have been exposed, and their doctrines brought to light, and these men refuted who have devised irreligious opinions. [I have accomplished this by adducing] something from the doctrine peculiar to each of these men, which they have left in their writings, as well as by using arguments of a more general nature, and applicable to them all. Then I have pointed out the truth, and shown the preaching of the Church, which the prophets proclaimed (as I have already demonstrated), but which Christ brought to perfection, and the apostles have handed down, from whom the Church, receiving [these truths], and throughout all the world alone preserving them in their integrity (bene), has transmitted them to her sons.
Then also— having disposed of all questions which the heretics propose to us, and having explained the doctrine of the apostles, and clearly set forth many of those things which were said and done by the Lord in parables— I shall endeavour, in this the fifth book of the entire work which treats of the exposure and refutation of knowledge falsely so called, to exhibit proofs from the rest of the Lord's doctrine and the epistles: [thus] complying with your demand, as you requested of me (since indeed I have been assigned a place in the ministry of the word); and, labouring by every means in my power to furnish you with large assistance against the contradictions of the heretics, as also to reclaim the wanderers and convert them to the Church of God, to confirm at the same time the minds of the neophytes, that they may preserve steadfast the faith which they have received, guarded by the Church in its integrity, in order that they be in no way perverted by those who endeavour to teach them false doctrines, and lead them away from the truth.
It will be incumbent upon you, however, and all who may happen to read this writing, to peruse with great attention what I have already said, that you may obtain a knowledge of the subjects against which I am contending. For it is thus that you will both controvert them in a legitimate manner, and will be prepared to receive the proofs brought forward against them, casting away their doctrines as filth by means of the celestial faith; but following the only true and steadfast Teacher, the Word of God, our Lord Jesus Christ, who did, through His transcendent love, become what we are, that He might bring us to be even what He is Himself.
Source: Adversus haereses (New Advent)