Only those churches established by the Apostles and their line of succession can be apostolic

…after first bearing witness to the faith in Jesus Christ throughout Judæa, and founding churches (there), they next went forth into the world and preached the same doctrine of the same faith to the nations. They then in like manner founded churches in every city, from which all the other churches, one after another, derived the tradition of the faith, and the seeds of doctrine, and are every day deriving them, that they may become churches. Indeed, it is on this account only that they will be able to deem themselves apostolic, as being the offspring of apostolic churches.

Tertullian
Against Marcion
The Prescription Against Heretics
Chapter XX

Christ’s substance is both man and God

Christ Jesus our Lord (may He bear with me a moment in thus expressing myself!), whosoever He is, of what God soever He is the Son, of what substance soever He is man and God, of what faith soever He is the teacher, of what reward soever He is the Promiser, did, whilst He lived on earth, Himself declare what He was, what He had been, what the Father’s will was which He was administering, what the duty of man was which He was prescribing; (and this declaration He made,) either openly to the people, or privately to His disciples, of whom He had chosen the twelve chief ones to be at His side, and whom He destined to be the teachers of the nations.

Tertullian
Against Marcion
The Prescription Against Heretics
Chapter XX

Scripture cannot be properly interpreted outside the Apostolic churches

Our appeal, therefore, must not be made to the Scriptures; nor must controversy be admitted on points in which victory will either be impossible, or uncertain, or not certain enough. But even if a discussion from the Scriptures should not turn out in such a way as to place both sides on a par, (yet) the natural order of things would require that this point should be first proposed, which is now the only one which we must discuss: “With whom lies that very faith to which the Scriptures belong. From what and through whom, and when, and to whom, has been handed down that rule, by which men become Christians?” For wherever it shall be manifest that the true Christian rule and faith shall be, there will likewise be the true Scriptures and expositions thereof, and all the Christian traditions.

Tertullian
Against Marcion
The Prescription Against Heretics
Chapter XIX

Heretics add and subtract from Scripture, and come up with new interpretations

Now this heresy of yours does not receive certain Scriptures; and whichever of them it does receive, it perverts by means of additions and diminutions, for the accomplishment of it own purpose; and such as it does receive, it receives not in their entirety; but even when it does receive any up to a certain point as entire, it nevertheless perverts even these by the contrivance of diverse interpretations. Truth is just as much opposed by an adulteration of its meaning as it is by a corruption of its text. Their vain presumptions must needs refuse to acknowledge the (writings) whereby they are refuted. They rely on those which they have falsely put together, and which they have selected, because of their ambiguity. Though most skilled in the Scriptures, you will make no progress, when everything which you maintain is denied on the other side, and whatever you deny is (by them) maintained. As for yourself, indeed, you will lose nothing but your breath, and gain nothing but vexation from their blasphemy.

Tertullian
Against Marcion
The Prescription Against Heretics
Chapter XVII

Heresies always arise out of a twisting of the Scriptures

When men, therefore, are not Christians even on their own admission, how much more (do they fail to appear such) to us! What sort of truth is that which they patronize, when they commend it to us with a lie?  Well, but they actually treat of the Scriptures and recommend (their opinions) out of the Scriptures! To be sure they do. From what other source could they derive arguments concerning the things of the faith, except from the records of the faith?

Tertullian
Against Marcion
The Prescription Against Heretics
Chapter XIV

A synopsis of the Apostolic faith

Now, with regard to this rule of faith—that we may from this point acknowledge what it is which we defend—it is, you must know, that which prescribes the belief that there is one only God, and that He is none other than the Creator of the world, who produced all things out of nothing through His own Word, first of all sent forth; that this Word is called His Son, and, under the name of God, was seen “in diverse manners” by the patriarchs, heard at all times in the prophets, at last brought down by the Spirit and Power of the Father into the Virgin Mary, was made flesh in her womb, and, being born of her, went forth as Jesus Christ; thenceforth He preached the new law and the new promise of the kingdom of heaven, worked miracles; having been crucified, He rose again the third day; (then) having ascended into the heavens, He sat at the right hand of the Father; sent instead of Himself the Power of the Holy Ghost to lead such as believe; will come with glory to take the saints to the enjoyment of everlasting life and of the heavenly promises, and to condemn the wicked to everlasting fire, after the resurrection of both these classes shall have happened, together with the restoration of their flesh. This rule, as it will be proved, was taught by Christ, and raises amongst ourselves no other questions than those which heresies introduce, and which make men heretics.

Tertullian
Against Marcion
The Prescription Against Heretics
Chapter XIII

What has Athens to do with Jerusalem? The early church refused to be influenced too heavily by pagan philosophy.

From all these, when the apostle would restrain us, he expressly names philosophy as that which he would have us be on our guard against. Writing to the Colossians, he says, “See that no one beguile you through philosophy and vain deceit, after the tradition of men, and contrary to the wisdom of the Holy Ghost.” He had been at Athens, and had in his interviews (with its philosophers) become acquainted with that human wisdom which pretends to know the truth, whilst it only corrupts it, and is itself divided into its own manifold heresies, by the variety of its mutually repugnant sects. What indeed has Athens to do with Jerusalem? What concord is there between the Academy and the Church? what between heretics and Christians? Our instruction comes from “the porch of Solomon,” who had himself taught that “the Lord should be sought in simplicity of heart.” Away with all attempts to produce a mottled Christianity of Stoic, Platonic, and dialectic composition! We want no curious disputation after possessing Christ Jesus, no inquisition after enjoying the gospel! With our faith, we desire no further belief. For this is our palmary faith, that there is nothing which we ought to believe besides.

Tertullian
Against Marcion
The Prescription Against Heretics
Chapter VII

The Church will never be overcome by heresies

Heresies, at the present time, will no less rend the church by their perversion of doctrine, than will Antichrist persecute her at that day by the cruelty of his attacks, except that persecution make seven martyrs, (but) heresy only apostates. And therefore “heresies must needs be in order that they which are approved might be made manifest,” both those who remained stedfast under persecution, and those who did not wander out of their way into heresy.

Tertullian
Against Marcion
The Prescription Against Heretics
Chapter IV

Holy orders mentioned. Salvation can be lost.

But what if a bishop, if a deacon, if a widow, if a virgin, if a doctor, if even a martyr, have fallen from the rule (of faith), will heresies on that account appear to possess the truth? Do we prove the faith by the persons, or the persons by the faith?  No one is wise, no one is faithful, no one excels in dignity, but the Christian; and no one is a Christian but he who perseveres even to the end.

Tertullian
Against Marcion
The Prescription Against Heretics
Chapter III