1 But again, we allege the same against those who do not recognise Paul as an apostle: that they should either reject the other words of the Gospel which we have come to know through Luke alone, and not make use of them; or else, if they do receive all these, they must necessarily admit also that testimony concerning Paul, when he (Luke) tells us that the Lord spoke at first to him from heaven: “Saul, Saul, why do you persecute Me? I am Jesus Christ, whom you persecute,” and then to Ananias, saying regarding him: “Go your way; for he is a chosen vessel unto Me, to bear My name among the Gentiles, and kings, and the children of Israel. For I will show him, from this time, how great things he must suffer for My name's sake.” Those, therefore, who do not accept of him [as a teacher], who was chosen by God for this purpose, that he might boldly bear His name, as being sent to the forementioned nations, do despise the election of God, and separate themselves from the company of the apostles. For neither can they contend that Paul was no apostle, when he was chosen for this purpose; nor can they prove Luke guilty of falsehood, when he proclaims the truth to us with all diligence. It may be, indeed, that it was with this view that God set forth very many Gospel truths, through Luke's instrumentality, which all should esteem it necessary to use, in order that all persons, following his subsequent testimony, which treats upon the acts and the doctrine of the apostles, and holding the unadulterated rule of truth, may be saved. His testimony, therefore, is true, and the doctrine of the apostles is open and steadfast, holding nothing in reserve; nor did they teach one set of doctrines in private, and another in public.
2. For this is the subterfuge of false persons, evil seducers, and hypocrites, as they act who are from Valentinus. These men discourse to the multitude about those who belong to the Church, whom they do themselves term “vulgar,” and “ecclesiastic.” By these words they entrap the more simple, and entice them, imitating our phraseology, that these [dupes] may listen to them the oftener; and then these are asked regarding us, how it is, that when they hold doctrines similar to ours, we, without cause, keep ourselves aloof from their company; and [how it is, that] when they say the same things, and hold the same doctrine, we call them heretics? When they have thus, by means of questions, overthrown the faith of any, and rendered them uncontradicting hearers of their own, they describe to them in private the unspeakable mystery of their Pleroma. But they are altogether deceived, who imagine that they may learn from the Scriptural texts adduced by heretics, that [doctrine] which their words plausibly teach. For error is plausible, and bears a resemblance to the truth, but requires to be disguised; while truth is without disguise, and therefore has been entrusted to children. And if any one of their auditors do indeed demand explanations, or start objections to them, they affirm that he is one not capable of receiving the truth, and not having from above the seed [derived] from their Mother; and thus really give him no reply, but simply declare that he is of the intermediate regions, that is, belongs to animal natures. But if any one do yield himself up to them like a little sheep, and follows out their practice, and their “redemption,” such an one is puffed up to such an extent, that he thinks he is neither in heaven nor on earth, but that he has passed within the Pleroma; and having already embraced his angel, he walks with a strutting gait and a supercilious countenance, possessing all the pompous air of a cock. There are those among them who assert that that man who comes from above ought to follow a good course of conduct; wherefore they do also pretend a gravity [of demeanour] with a certain superciliousness. The majority, however, having become scoffers also, as if already perfect, and living without regard [to appearances], yea, in contempt [of that which is good], call themselves “the spiritual,” and allege that they have already become acquainted with that place of refreshing which is within their Pleroma.
3. But let us revert to the same line of argument [hitherto pursued]. For when it has been manifestly declared, that they who were the preachers of the truth and the apostles of liberty termed no one else God, or named him Lord, except the only true God the Father, and His Word, who has the pre-eminence in all things; it shall then be clearly proved, that they (the apostles) confessed as the Lord God Him who was the Creator of heaven and earth, who also spoke with Moses, gave to him the dispensation of the law, and who called the fathers; and that they knew no other. The opinion of the apostles, therefore, and of those (Mark and Luke) who learned from their words, concerning God, has been made manifest.
Source: Adversus haereses (New Advent)