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An Old Heresy Is New Again

An Old Heresy Is New Again

Last updated on: January 18, 2026 at 11:55 am by David Schloss

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An Old Heresy Is New Again 2026-01-18T11:55:03-05:00 David Schloss

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On Heresy.

The axiom “there is nothing new under the sun” is only sometimes true. In the case of heresy, however, it seems to be all but certain. One such old heresy that is proving resilient is Unitarianism.

This essay will examine the beliefs and history of Unitarianism by placing it in contrast with the orthodox belief of Trinitarianism. To do that requires an explanation of the Holy Trinity.

Trinitarianism And Orthodoxy

Without question, explaining the Holy Trinity is a difficult task for any theologian. Nevertheless, Catholic theology asserts that God is one being (essence) existing as three coequal and eternal persons: Father, Son, and Holy Spirit. All three persons of the Trinity are fully Divine, eternal, and equal in power, glory, and majesty.

God the Father is the principle without principle, which is to say that God the Father is not caused or generated by another. This concept of the Father as the uncaused cause is essential in understanding the relations between the Father, the Son, and the Holy Spirit.

The foundations of the Trinitarian doctrine can be found in the overall pattern of Divine activity to which the Scripture bears witness. Moreover, the shape of Trinitarian doctrine is dictated by the pattern of redemption. Everything comes from the Father, is made known and redeemed by Jesus Christ, and is consummated by the power of the Holy Spirit.

When we consider the Trinity, we are seeking insights into the inner life of God. One of Saint Augustine’s insights is that the Father knows Himself through His reason (logos), and this is Christ. In knowing Himself, He loves Himself, and this is the Holy Spirit.

How, then, do the Trinity relate to one another? The Father eternally generates the Son and, as such, Christ is the Second Person of the Holy Trinity. The Father and the Son actively spirate the Holy Spirit into the one relation within the inner life of God. Spirated, not generated, because the Father and Son are already constituted as persons concerning each other in the first two relations. For this reason, the Catechism teaches that “The second person of the Blessed Trinity is Son only in relation to his Father.” (Catechism of the Catholic Church, Paragraph 240).

The Holy Spirit, therefore, is the love between the Father and Son. Because of this fact, the Holy Spirit is spirated of the Father and the Son, constituting the Person of the Holy Spirit. Put differently, the Holy Spirit proceeds from the Father and the Son, but not in a generative sense, but as a spirit or breath.

The Catholic Church’s Trinitarian doctrine of one God in three coequal, coeternal persons developed gradually from early Christian scriptures and traditions. It was formally defined at the First Council of Nicaea (325 AD) and was solidified at the Council of Constantinople (381 AD).

While these various councils sought to affirm the Divine nature of Jesus and the Spirit alongside the Father through key philosophical terms such as “substance,” “essence,” and “person,” the councils were also responding to various errors promulgated in the years following the Ascension of Christ. One such error is Unitarianism.

Unitarianism

These terms – Trinitarianism and Unitarianism – are foundational to theology and our understanding of the God depicted in the Bible. Specifically, the terms denote the number of persons that share the Divine essence. To understand the conflicting positions of Trinitarianism and Unitarianism, it is necessary to distinguish between essence and existence.

Essence is the “whatness” or nature of a thing, while existence is the actualization of a specific essence, generally within a person or animal. It is, therefore, possible to discuss the universal nature of ‘humanity’ distinctly from the billions of individual persons who possess it. As it applies to God, theology can examine the Divine essence of God (albeit in a very limited way) without necessarily applying it to the person or persons that share that essence.

Having set the groundwork, so to speak, what does Unitarianism assert?

The fundamental claim of Unitarianism is that God is one. One not just in essence but in existence or personhood. As such, Unitarianism denies the Trinity and rejects the claim that Jesus is God. Unitarians teach that Jesus was an inspired man, a great teacher, and an example to follow, but not God.

Having provided a brief synopsis of Trinitarianism and Unitarianism, we can examine why the Catholic Church considers Unitarianism a heresy.

The Problem With Unitarianism

Interestingly, Unitarians often take a positive view of the term heretic, noting that it derives from the Greek word meaning choice. The idea being that Unitarians, as heretics, are free to interpret Scripture and faith through human reason, rather than accepting the teachings of the Church.

Unfortunately, the belief that one should interpret Scripture independently of both Divine revelation and the Church created by God lends itself to heresy. Scripture itself warns against this view. “Trust in the Lord with all your heart; on your own intelligence do not rely.” (Proverbs 3:5). As suggested by the title of this paper, Unitarian and non-Trinitarian heresies are not new. These beliefs circulated throughout the early church.

The rejection of the Holy Trinity in general and the denial of Christ’s divinity specifically have led the Catholic Church to deem Unitarianism a heresy.

Despite its condemnation, Unitarianism has persisted in various forms. In the years following the Protestant Reformation, Unitarianism seemed to undergo a revival of sorts as various groups felt freer to break with the official Catholic doctrine of Trinitarianism. Regardless, the modern version of Unitarianism is essentially a rehash of the fourth-century Arian heresy.

In addition to rejecting the Trinity, some versions of Unitarianism have also rejected the Bible as a form of Divine revelation in favor of human reason. In effect, Unitarianism generally favors horizontal relationships between human beings over vertical relationships between God and human beings. Ultimately, there are three fundamental reasons why Catholicism rejects Unitarianism.

The first reason is its rejection of the Trinity. The doctrine of the Trinity is the central and most fundamental teaching of Catholicism. Moreover, a Trinitarian understanding of God influences every aspect of Catholic theology.

The second reason why Unitarianism is antithetical to Catholicism involves Christology. The Unitarian denial of Christ’s Divinity stands athwart the Catholic and biblical teaching of Jesus as the Son of God and as the second person of the Trinity. Furthermore, the hypostatic union is the structure that makes salvation possible. If Christ is not God and man, then He cannot and has not made salvation possible.

Finally, Unitarianism conflicts with the Nicene Creed, which established the Trinity as dogma and effectively labeled non-Trinitarian views as heresy.

Conclusion

A Unitarian theology does significant damage to the Christian understanding of God as depicted in the Bible and through Divine revelation. That, in and of itself, is sufficient reason to reject it.

However, by denying the divinity of both Christ and the Holy Spirit, Unitarianism makes the salvific work of the Trinity null and places the faithful in danger of damnation by rejecting the need for faith in Christ (John 11:25).

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