I often write about how the Church’s authority is important, especially when it comes to sorting out and teaching the Truths of the Faith, since we often get it wrong when we try to do it ourselves. You can fnd an in -depth examination on the three sources of authority in the Catholic Church – Scripture, Tradition, Magisterium – here. In this two-part series, I will explain yet another reason why we need the authority of the Church to protect the truth of who Jesus is and what we believe about Him: heresy.

Let’s start with the definition of heresy. The Catechism states:

Heresy is the obstinate post-baptismal denial of some truth which must be believed with divine and catholic faith, or it is likewise an obstinate doubt concerning the same. (CCC #2089)

Essentially, after a person is baptized and initiated into the Church, they are to give their assent to the truths the Church teaches, with the understanding that it is the Church’s mission to lead souls to heaven and not astray. Another key component of being a heretic, or a person committing heresy, is the refusal to be corrected. A person with an incorrect belief but who is open to understanding and conversion, or an unaware person, would not be committing heresy. As an aside, the Church defines many degrees and types of heresy, but that is beyond the scope of this article, so we’ll just stick with the simple definition here.

For as long as the Church has existed, there have been individuals around to say that what the Church teaches about this or that is incorrect, and “this” is what it should be teaching instead. Even today, there are plenty of heresies floating around and they are best to be ignored. In terms of the development of the Magisterium (the teaching office and authority of the Church), heresies do, however, serve a great purpose, as they raise questions that allow for clarification and more solidified doctrine. There were many, but I will give an overview of just three big heresies — Gnosticism, Arianism, and Nestorianism — that entered into the very early Church and played a role in defining the truths we take for granted today.


Gnostic comes from the Greek word gnosis, which means “knowledge.” Thus, Gnostics were “those who know.” Rather than having precise doctrine, Gnosticism was more of a fluid form of enlightenment resulting in varying belief systems and practices. They believed in a Supreme Being, but that He was distant and impersonal. This Supreme Being created lesser gods. Then the material world was created by an evil, lesser god. Therefore, all matter, including human flesh, was considered evil. For this reason, it was thought that the emphasis should be on man as a spiritual being since his physical body has no value. As for the person of Jesus Christ, they believed that a good spiritual God would never take on human flesh, so He just sort of took on the disguise of Jesus. According to Gnostics, it also would not be appropriate for Him to come to us in the form of bread and wine in the Eucharist. As for their enlightenment, they believed that Jesus had revealed certain spiritual knowledge to a specific group of people and that the followers of the Apostles were practicing an inferior form of Christianity. This special knowledge was then passed on to the Gnostics. You might recognize modern-day forms of Gnosticism in the New Age movement or when you hear someone say, “I’m spiritual, but not religious.”

The Church’s great champion in fighting Gnosticism was St. Irenaeus of Lyon (c. 130- 202 AD), who wrote a five-book treatise entitled, Against Heresies. In it, St. Irenaeus explains how man is not just a spiritual being, but a composite of spiritual and physical. Therefore, the Incarnation of God in Jesus was not merely appropriate, it was also fitting for man’s salvation. He entered into the world to be present with us and to live in the same manner we live, teaching us the things necessary for our spiritual well-being while in the flesh. St. Irenaeus was, likewise, teaching about the true presence of Jesus in the Eucharist and how the reality of God does, in fact, continually come to us through matter saying, “For as the bread from the earth, receiving the invocation of God, is no longer common bread but the Eucharist… so also our bodies, when they receive the Eucharist, are no longer corruptible but have the hope of resurrection into eternity.” With regard to the claim that certain people had special knowledge from Jesus that others did not possess, St. Irenaeus was able to demonstrate that the only way to protect truth and teaching is through apostolic succession, rather than secret communications between privileged groups. Apostolic Succession is the teaching of the Church in which Jesus passed on the Faith to His apostles, who then passed it on to their successors and so on. This creates an unbroken chain of succession that continues through today. Irenaeus was writing around 185 AD, so he was able to demonstrate an unbroken list of 12 Bishops of Rome (popes) who all came one by one after the first, the Apostle Peter, appointed by Christ Himself. So, you can thank St. Irenaeus for his contributions to the Church’s firm doctrines of the Incarnation, the Eucharist, and Apostolic Succession (among many others).

This week, reflect on how incorrect beliefs can so easily seep into humanity. We continue to see it every day. We have a great gift in the Catholic Church, established by Jesus Christ Himself, which has been protected by the Holy Spirit, as promised, throughout history. Be grateful for that gift. Also, think of a doctrine that you have difficulty accepting or believing. Ask God to open your heart and mind to obtain a deeper understanding of its truth. Approach Him in faith!

Next week we’ll examine the two heresies of Arianism and Nestorianism and how the Church dealt with them.

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Heresies – Using Error to Clarify Divine Truth (Part 2)