For instance, consider what he said in the introduction to his extensive literary work entitled “The Refutation and Overthrow of the Knowledge Falsely So Called.” He wrote: “Certain men, rejecting the truth, are introducing among us false stories and vain genealogies, which serve rather to controversies, as the apostle said [1 Timothy 1:3, 4], than to God’s work of building up in the faith. By their craftily constructed rhetoric they lead astray the minds of the inexperienced, and take them captive, corrupting the oracles of the Lord, and being evil expounders of what was well spoken.”

Irenaeus’ principal work, “The Refutation and Overthrow of the Knowledge Falsely So Called,” was commonly referred to by the name “Against Heresies.” It is divided into five books. The first two contain a critical description of the beliefs of various heretical sects, particularly the Valentinian heresy. In the remaining three books, Irenaeus attempts to set forth “arguments from the Scriptures.”

In the introduction to his third book “Against Heresies,” Irenaeus writes: “Keep in mind therefore what I have said in the two previous books; and by adding this to them you will have from me a full reply against all heretics, and will be able to resist them faithfully and boldly on behalf of the one true and life-giving faith, which the Church has received from the apostles and imparts to her children. For the Lord of all gave to his apostles the power of the gospel, and by them we also have learned the truth, that is, the teaching of the Son of God​—as the Lord said to them, ‘He who hears you hears me, and he who despises you despises me, and him who sent me.’”

Although Irenaeus admitted that he was not a good writer, he was determined to expose all aspects of the “evil teachings” of Gnosticism. He quotes and comments on many scriptures and argues masterfully against the “false teachers” of the “destructive sects.” (2 Peter 2:1-3) It appears that Irenaeus had difficulty compiling his work into a satisfactory form. Why? Because he had amassed material of enormous proportions.

Irenaeus’ exposé was manifestly brought to birth after great pains and much study. His lengthy arguments supply a wealth of information on the sources and phenomena of Gnosticism. The writings of Irenaeus are also an invaluable index of at least some of the Scriptural views still held by professed adherents to God’s Word at the end of the second century C.E.

Irenaeus repeatedly reaffirms belief in “one God, the Father Almighty, who made the heaven, and the earth, and the seas, and all that is in them, and in one Christ Jesus, the son of God, who was made flesh for our salvation.” These facts the Gnostics denied!

Speaking against Gnostic Docetism (the teaching that Christ never came in human form), Irenaeus wrote: “Christ must be a man, like us, if he would redeem us from corruption and make us perfect. As sin and death came into the world by a man, so they could be blotted out legitimately and to our advantage only by a man; though, of course, not by one who should be a mere descendant of Adam, and thus himself stand in need of redemption, but by a second Adam, supernaturally begotten, a new progenitor of our race.” (1 Corinthians 15:45) On the other hand, the Gnostics were Dualists, believing that spiritual things were good but that all matter and flesh were evil. Consequently, they rejected the man Jesus Christ.

Reasoning that all flesh is evil, the Gnostics also rejected marriage and procreation, claiming that Satan originated these. They even ascribed divine wisdom to the serpent in Eden! This viewpoint resulted in extreme life-styles, either asceticism or fleshly indulgence. Claiming that salvation came only through mystical Gnosticism, or self-knowledge, they left no room for the truth of God’s Word.

In contrast, Irenaeus’ arguments included belief in the Millennium and indicated some comprehension of the prospect of peaceful future life on earth. He endeavored to unite the growing factions of his time by wielding the powerful Word of God. And he is generally remembered for his clear thinking, acute perception, and sound judgment.

Although some credit Irenaeus (who died about 200 C.E.) with fostering the true doctrines of the Christian faith, it must be remembered that his was a time of change and foretold apostasy. At times, his arguments are somewhat vague, even contradictory. Nevertheless, we highly value the testimony of men who boldly spoke out in favor of the inspired written Word of God rather than the traditions of men.