The Anti-Heretical Literature of the Second Century
Mainly the heresies of the very beginning were : Gnosticism, Marcionism, Montanism and Judaism. They were a threat not against the existence but against the purity and integrity of Christianity.
The term is generic and includes a great variety of teachings. Based on the theory of a dual principle, it rejected creation :
Marcionism is a tempered form of Gnosticism.
Authors: Cerdo, who came to Rome as disciple of Valentinus and Marcion, son of the bishop of Sinope, in Pontus, who cast him out of the Church. Marcion came to Rome (c. 135) and gave much money to the poor and was received into the Church and soon cast out again for teaching heresy. His teaching is Gnostic. He rejected the Old Testament as the work of a rigidly just, cruel and vindictive God. He taught the New Dispensation as the work of a good God and asserts it is being corrupted by Jewish efforts. He retains along Gnostic dualism and Docetism with a rigid moral teaching. His teaching was formidable, successful. Tertullian called him `the Wolf of Pontus' : he did much harm to the Christian flock. A separate Church organised by him survived until the fifth century.
Montanism opposed the authority of the Christian hierarchy directly by its profession of prophecy (Gnosticism had opposed the teaching of the hierarchy with its own teaching).
In the second century the charisms had practically disappeared. The Phrygian, Montanus, feigned to restore them. Shortly after his baptism he began to prophesy (c. 156 or 172) but convulsions and ecstasies attended his prophecies. He announced himself as the organ of the Holy Ghost (the fulfilment of `I will send you a Paraclete'), and his prophecies and revelations were to supersede Christ’s revelation. They taught the imminence of the Second Coming and Christ’s reign for a thousand years.
Moral teaching was austere and set aside allowance Christ made for the flesh : Second marriages were forbidden (and first marriages at the beginning), more fasts, sins committed after baptism were not forgiven. The chute lamentable of Tertullian is one of the chief reasons for their importance. They split up into several sects, Montanists according to Proclus, to Aeschines etc., and the most celebrated sect was the Tertullianists.
Mainly, they wanted to keep the Judaic practises with Christian Faith and liturgy.
Saint Irenaeus was a native of Asia (between 120 and 140). He had listened to many presbyters, the immediate disciples of the Apostles, and among them especially Saint Polycarp. Together with his attachment to tradition which he had learnt from Saint Polycarp, and his love of the Scriptures which he knew perfectly, he was best characterised by the depth of his faith and the breadth of his knowledge. He was highly educated and had read many Greek authors, both literary and philosophical. He made a special point of knowing all the heresies in order to refute them and render more certain the triumph of the true faith.
In the year 177, he was a priest of the Church of Lyons, governed by Saint Pothinus. He was charged to bring a letter to Rome to Pope Eleutherius (175-189). It was probably this journey to Rome which saved him from the persecution that broke out in Lyons in 177-178, and of which Saint Pothinus was the most illustrious victim. Irenaeus must have occupied an important place in the Church at Lyons for on his return from Rome he was chosen to succeed Saint Pothinus.
The apostolate of Saint Irenaeus took on three forms. Of these three his struggles against Gnosticism are the most glorious. This heresy was ravaging Gaul as well as Italy and the East, from whence it had probably been brought by travellers. At the request of a friend, a priest and perhaps a bishop, of Greek origin and knowing Greek, Saint Irenaeus made a point of exposing the Gnostic doctrines, for “to reveal their system is to vanquish them”. This first writing was soon followed by four others containing a direct refutation, which together form the Adversus Haereses. The real title was The false Gnosis unmasked and refuted.
Saint Irenaeus also laboured to spread Christianity in the provinces adjacent to Lyons. There is no doubt that, in spite of the relative youth of this Church founded by Saint Pothinus, the vigorous personality of its bishop helped Lyons to become the Christian metropolis of Gaul as it was already the political metropolis. Churches of Besançon and Valence, claim that Saint Irenaeus was the first to announce the Gospel to them.
The intervention of Saint Irenaeus in the Easter Controversy about 190 in the time of Pope Victor (189-198), was of considerable importance. The Church of Asia Minor was accustomed to celebrate Easter on the 14th Nisan (the lunar month of March) as did the Jews ; Rome celebrated it the following Sunday. Pope Victor made up his mind to put an end to the controversy and, at his request, councils were held throughout the whole Church. They all accepted the Roman date, save the Asian bishops and Polycrates, Bishop of Ephesus. Pope Victor was to excommunicated these bishops but Irenaeus, who thought this was going too far, intervened with the Pope in their favour. The Church of Asia adopted the Roman use in its turn and followed it, at least from the beginning of the fourth century.
According to Tradition, he died Martyr  in 202-203. In 1562 his remains were scattered by the Calvinists, and only his head has been refound.
1) The extant works of Saint Irenaeus are as follows :
- On the Monarchy or How God is not the Cause of Evil, written against Florinus, a former friend who had become a Gnostic.
- On the Ogdoad (against the Ogdoad of Valentinus), addressed to Florinus.
- Treatise on Schism (quarto-deciman), to Blastus, a friend of Florinus.
- Letter to Pope Victor, on the Eastern question.
- On the Subject of Knowledge, a “short but necessary book”(Eusebius) this little apology to the Greeks.
- Divers discourses (treatises or perhaps homilies).
- Some writings have been wrongly attributed to him .
2) The Proof of the Apostolic Preaching
It is a popular exposition of the faith and its proofs, a direct and summary presentation of Catholic doctrine. It is certainly brief, but, it is full of an extraordinary Christian feeling, at the same time simple, confident and profound. In some ways this work completes the Adversus Haereses ; but on the whole it unfolds the same ideas.
3) The Adversus Haereses
This work, in five books, was originally meant to be a short exposition of Valentinianism together with its refutation, to comply with the request of a friend. This first plan, however, gradually developed.
The first book exposes what are the Valentinian systems (of Valentinus himself, Ptolemy, his disciple, and Marcus, a Gallic Gnostic) and what were the origins of Gnosticism from Simon Magus. He exposes Valentinianism, as the culminating point of all past heresies, and also gives an account of the various derived sects.
The second offers the philosophical and rational refutation. By means of vigorous logic, Saint Irenaeus proves to the Gnostics that their system must lead them to two equally impossible explanations: Dualism or Pantheism.
In the three following books, Saint Irenaeus exposes of the true doctrine, of which he constructs a vast synthesis in order to demonstrate its superiority over the Gnostic doctrines. He presents the positive refutation of historical errors which are directly opposed to the teachings of the Scriptures. This new demonstration by a masterly explanation of considerable theological importance of the Catholic rule of faith. All these three books are extremely rich in doctrine and have merited for Saint Irenaeus the title of “Father of Catholic theology”.
C) The doctrine of Saint Irenaeus.
Saint Irenaeus exercised a great doctrinal influence : he killed Gnosticism ; he founded Christian theology.
By the Adversus Haereses, Gnosticism was not immediately vanquished ; there were attempts at a recovery in the third and even in the fourth century. But the blows of Saint Irenaeus had been effective and the error was laid.
At the same time he founded Christian theology and based it solidly on Scripture and Tradition, establishing the rule of faith and placing his confidence in the “charisma of truth” which renders the Church indefectible. He was also the founder of theology by his synthetic exposition of revealed truth. His doctrine can be classed under five heads : The rule of faith ; God and the Trinity ; Christ and the Redemption ; Spiritual life ; The last ends.
1) The Rule of Faith.
It may be summed up in the following propositions :
- The exact interpretation of the Scriptures, which are the source of faith, requires a “fixed rule of faith” ; this rule of faith is the baptismal symbol, or more exactly, Christian faith itself, expressed in the Creed and taught throughout the Church.
- The duty of fixing the exact form of this symbol and of giving the true explanation of it properly belongs to the Church, which has received the Holy Ghost for the purpose of safeguarding and spreading religious truth without error : Ubi enim Ecclesia, ibi est Spiritus Dei et ubi Spiritus Dei, illic Ecclesia et omnis Gratia : Spiritus autem veritas.
- The true teaching of the Church is that which is given by the actual pastors, who have received it from the Apostles by way of uninterrupted tradition. It is that of the Mother-Churches who can show a catalogue of their bishops going back to the beginnings of Christianity : to sum up, the rule of faith is the present, living magisterium of the Church.
- Since any enquiry into the teaching of all the Churches is beset with difficulty, there remains a last criterion of truth which is in reach of everybody and which is sufficient : it is the teaching of the Church of Rome.
So doing, St Irenaeus He gives a clear expression of the doctrinal unity of the universal Church, of the unique and sovereign importance of the Roman Church as the witness, guardian and organ of the Apostolic tradition and of its superior pre-eminence in the whole of Christendom :
In his struggle against Gnosticism which made a distinction between a supreme God and a Demiurge, Saint Irenaeus was obliged to insist on the unity of God, infinitely holy and perfect by His nature, creator of an ordered and harmonious world, since disorder does not derive from the author of nature.
This simplicity and unity of essence, however, does not exclude the Trinity. Saint constantly names the three Persons and always places Them in the first rank. The plenitude of the divinity, everlastingly on the lips of the Gnostics, is expressed by the Father, the Word and the Holy Ghost; God created everything through the Word and the Holy Ghost, but this Word and this Spirit are one with God.
As it was for Saint Paul, Christology is the centre, the heart of all the theology of Saint Irenaeus.
- The principle of all his Christology is the doctrine of recapitulation to which he was particularly attached. Saint Irenaeus is aware of the personal unity of Christ and the duality of His nature, and he shows this by his extensive use of the communication of idioms. Moreover, it is necessary that Christ should be God in order to fulfil His mission in the world.
- Christ has a threefold mission :
- He is the revealer, the author of the fourth and the last Testament (the first three were given to Adam, to Noe and to Moses)
- He is the Redeemer, who by His obedience during His life and in His violent death makes expiation for our sins and vanquishes the devil
- He is the deifier, the sanctifier who reconciliates us with God, makes us again in His image, makes us children of God, and, lastly, confers immortality and everlasting life upon us.
- The fruits of the Redemption are produced in this life a lively and operative faith, by baptism (which is conferred even on little children), and above all by the Eucharist which is not only as a Sacrament but also an oblation, a sacrifice, which renews the whole mystery of the Redemption.
- The doctrine of Mary’s share in the work of Redemption, first developed by Saint Justin, was continued and completed by Saint Irenaeus. After having made a parallel between Adam and Jesus Christ, he opposes the reparative action of the second Eve, Mary, to the death-bringing work of the first.
“Mary loosened the knots formed by the fault of Eve. The one resisted the commands of God, the other submitted to them. Eve listened to the voice of the Devil, Mary gave heed to the voice of the Angel. The human race, sent to its death by a virgin, has been saved by another virgin” 
Saint Irenaeus affirms Mary’s divine maternity and her perpetual virginity.
4) Christian spirituality
Saint Irenaeus opposed a Christian conception of spirituality to the false Gnostic asceticism. ; as in the teaching of Saint Paul, the Holy Ghost occupies a large place.
The Spirit is shown as a constitutive element of the perfect man : in the perfect man may be found, besides the three elements, body, soul and spirit , an intimate union with the Holy Ghost.
The part played by the Holy Ghost is to give back to man the resemblance to God and to the Son, which was lost by sin. No doubt man is free and can hinder this action, as did Adam. But man alone can do nothing to make himself like to God
5) The last things
The Eschatology of Saint Irenaeus is “a mixture of interesting ideas, of affirmations containing the substance of the Church’s teaching, and of contestable or even frankly erroneous theories. It is the weakest part of his work” .
He admitted the opinion, now heretical, of the postponement of the Beatific Vision until the General Judgement. He also believed that Christ would reign for a thousand years in this world, with the just arisen from the grave (Millenarianism). This millenarianism is used as an arm against Gnosticism. He defended it by saying that man must be led little by little, through a process of gradual ripening, to the vision of God. It was also a consequence of his doctrine of recapitulation.
 St Jerome is the first (in 410) to quote his martyrdom. Neither Tertullian, Hippolytus nor Eusebius mentions this fact. The silence of the early authors may be explained by the fact that if Irenaeus met his death in the general massacre of the Christians of Lyons under Septimius Severus his martyrdom would have attracted less notice than otherwise.
 Notably the four fragments published by Pfaff, a Protestant professor at Tubingen in the 18th century. Pfaff himself fabricated these pieces.
 Propter po[ten]tiorem principalitatem
 Adv. Haer. III, 3, 3
 Adv. Haer. III, 22, 3-4
 With the Greeks, St Irenaeus distinguished the soul and the spirit according to the two kind of functions of the soul : sensitive life and spiritual life.
 F. Vernet, Dictionnaire de Théologie, col 2498-2507.