St. Irenaeus is an incredibly important figure in the history of the church and the history of theology. He is beloved of Catholics, Orthodox, and Protestants (a rarity if ever there was one).

Irenaeus is a well-known figure for several reasons:

• He is one of the best links between the Apostolic period and the sub-Apostolic period
• He is one of the earliest and most developed examples of Christian theology as expressed outside of Holy Scripture
• He was important as a source for determining the content of Gnostic belief and practice in certain circles before the relatively-recent discovery of Gnostic primary texts
• He was martyred for his faith
• He is the beginning of Christian pre-millennial eschatology outside of Scripture
• He is important as an opponent of various heresies that plague the church to this day
• His “Against Heresies” (Latin: Adversus Haereses”) is a seminal text for discussions amongst Christians regarding questions of: submission to ecclesiastical authority; Apostolic Succession; the roles of presbyter and episkopos; “Catholicity”
• His work is important in the argument for purity in the textual transmission of Holy Scripture: Irenaeus quotes Scripture frequently (and alludes to it often) and his quotations match those of other manuscripts for the given verse

Ecclesiastes 1:9 says, “The thing that hath been, it is that which shall be; and that which is done is that which shall be done: and there is no new thing under the sun.” The kind of heresies that Irenaeus was fighting were really extensions of problems that had attacked the Gospel and the Church from the very beginning.

They were issues such as: refusal to obey the Apostles and their appointed representatives; disbelief in the deity of Christ; the Sonship of Christ and Fatherhood of God; disbelief in the Incarnation, that is the Word putting on true human flesh; disbelief in the value of the body; disbelief in the true human suffering and blood-flow of Christ in His sorrowful Passion; worship of angels and other “gods”; disbelief in the Resurrection; etc.

Evidence of these heresies can be found in the New Testament as things that the Apostles condemn. Three loci classici for this are Col. 2:18-19, Heb. 1:5, and 1 Jn. 2:22-23:

“Let no man beguile you of your reward in a voluntary humility and worshipping of angels, intruding into those things which he hath not seen, vainly puffed up by his fleshly mind, and not holding the Head, from which all the body by joints and bands having nourishment ministered, and knit together, increaseth with the increase of God.”

“For unto which of the angels said he at any time, Thou art my Son, this day have I begotten thee? And again, I will be to him a Father, and he shall be to me a Son?”

“Who is a liar but he that denieth that Jesus is the Christ? He is antichrist, that denieth the Father and the Son. Whosoever denieth the Son, the same hath not the Father: he that acknowledgeth the Son hath the Father also.”

To be somewhat bold in the statement of the facts, these heresies still exist today in some form or another in sects that masquerade as Christian and in other religions.

Jehovah’s Witnesses deny the deity of Christ and call Him the Archangel Michael: thus, if they worship Him, they are according to their own standard worshipping an angel and defying the commandment of God (Col. 2:22; Rev. 19:10).

Muslims deny the deity of Christ and utter the phrase “God does not beget, nor is He begotten”, an utter blasphemy to Christians. They deny that Christ died on the Cross, but believe that God substituted someone for Him (many believe Judas was put in His place as a punishment for betraying Christ) and took Christ into heaven like He did Elijah. Sufi Muslims believe in a process called fana, wherein a true worshipper becomes one with God and destroys his own ego, and thus can legitimately say, “I am God” (cf. 2 Thess. 2:4).

Buddhism denies the value of the material world that God has created, and teaches that man’s best path is to reach Nirvana, a state where he permanently escapes the world. This denial of the body flies in the face of the teaching of physical Resurrection championed by the Apostles. It is this Hellenistic, worldly spirit/principality/stoicheia that Paul met amongst the philosophers of Athens when he preached the Gospel:

“And when they heard of the resurrection of the dead, some mocked: and others said, We will hear thee again of this matter.” (Acts 17:32)

Here are some of the things Irenaeus had to say about such spiritual error and deception (taken from http://biblehub.com , translation Dr Roberts and Rev. W.H. Rambout).

“On this account, they tell us that it is necessary for us whom they call animal men, and describe as being of the world, to practise continence and good works, that by this means we may attain at length to the intermediate habitation, but that to them who are called “the spiritual and perfect” such a course of conduct is not at all necessary. For it is not conduct of any kind which leads into the Pleroma, but the seed sent forth thence in a feeble, immature state, and here brought to perfection.”

“You see, my friend, the method which these men employ to deceive themselves, while they abuse the Scriptures by endeavouring to support their own system out of them. For this reason, I have brought forward their modes of expressing themselves, that thus thou mightest understand the deceitfulness of their procedure, and the wickedness of their error. ”

“Learn then, ye foolish men, that Jesus who suffered for us, and who dwelt among us, is Himself the Word of God. For if any other of the Æons had become flesh for our salvation, it would have been probable that the apostle spoke of another. But if the Word of the Father who descended is the same also that ascended, He, namely, the Only-begotten Son of the only God, who, according to the good pleasure of the Father, became flesh for the sake of men, the apostle certainly does not speak regarding any other, or concerning any Ogdoad, but respecting our Lord Jesus Christ. For, according to them, the Word did not originally become flesh. For they maintain that the Saviour assumed an animal body, formed in accordance with a special dispensation by an unspeakable providence, so as to become visible and palpable. But flesh is that which was of old formed for Adam by God out of the dust, and it is this that John has declared the Word of God became. Thus is their primary and first-begotten Ogdoad brought to nought.”

While a familiarity with Irenaeus is not strictly necessary in learning to refute heresy, I would encourage people to have a little look at his work as an example of an early Christian obeying the instructions of the Apostles:

“But sanctify the Lord God in your hearts: and be ready always to give an answer to every man that asketh you a reason of the hope that is in you with meekness and fear” (1 Pet. 3:15).

At times the heresies of the Gnostics and their ilk may seem irrelevant to us as we read Paul’s exhortations or Irenaeus’ refutations – but the missionaries who work in Muslim lands can tell you otherwise. Forewarned is forearmed.