In order to do some justice to this sublime subject, we shall look only briefly at the heretical positions that at various periods of the Church’s history challenged the revealed Trinitarian faith. Our principal intention is to see in sequence the development of the doctrine, with emphasis on how the Church’s authority has contributed to the progress in understanding the plurality of persons in the one true God. 

There is also great value in seeing some of the implications of the doctrine for our personal and social lives, since the mystery was most extensively revealed by Christ during the same discourse at the Last Supper when He taught us the “New Commandment” by which we are to love one another as He has been loving us.

Trinitarian Heresies
There is a certain logic in the adversative positions assumed by those who called into question one or another aspect of the Trinity. Not surprisingly the human mind has wrestled with what God revealed about Himself in His inner Trinitarian existence. And depending on the willingness to recognize its limitations, the intellect has been enlightened by what God says about His mysterious being.

Thus we have, on the one hand, such extensive treatises as St. Augustine’s De Trinitate that show how perfectly compatible is the mystery of the Triune God with the deepest reaches of human intelligence. Indeed, the better the Trinity is understood, the more the human mind expands its horizons and the better it understands the world that the Trinity has created.

At the same time, we have the spectacle of another phenomenon. Minds that are not fully docile to the faith have, in greater or less measure, resisted the unquestioning acceptance of the Trinity. From apostolic times to the present, they have struggled with themselves and in their misguided effort to “explain” the mystery have only rationalized their own ideas of what the mystery should be.

For the sake of convenience, we can capsulize the leading anti-Trinitarian teachings of Christian history. Although given here somewhat chronologically, they are all very current because one or another, or a combination of several, may be found in contemporary writings in nominally Christian sources. There is no such thing as an antiquated doctrinal error, as correspondingly there is no such thing as an entirely new heresy. Error has its own remarkable consistency.

Monarchianism
By the end of the first century, certain Judaizing Christians lapsed into a pre-Christian notion of God. According to them God is simply unipersonal. Such were the Corinthians and the Ebionites. 

Within the next hundred years these theories were systemized into what has since become known as Monarchianism, i.e., monos = one + archein = to rule, which postulates only one person in God. In practice, however, Monarchianism affected certain positions regarding the nature and person of Christ; and these were the ones that finally had to be countered by the Church’s Magisterium.

If there is only one person in God, then the Son of God did not become man except as the embodiment of an adopted son of God. According to the Adoptionists, Christ was a mere man, though miraculously conceived of the Virgin Mary. At Christ’s baptism, He was endowed by the Father with extraordinary power and was then specially adopted by God as son. Among others, the best known Adoptionist was Paul of Samosata. 

Another group of Monarchians took the view that Christ was divine. But then it was the Father who became incarnate, who suffered and died for the salvation of the world. Those favoring this idea were called Patripassionists, which literally means “Father-sufferers,” meaning that Christ was only symbolically the son of God, since it was the Father Himself who became man. On this hypothesis, of course, the Father, too, is only symbolically Father, since He does not have a natural Son.

The best known Patripassionist was Sabellius, who gave his name to a still popular Christological heresy, Sabellianism. According to Sabellius, there is in God only one hypostasis (person) but three prosopa, literally “masks” or “roles” that the unipersonal God assumes. These three roles correspond to the three modes or ways that God manifests Himself to the world. Hence another name for this theory is Modalism.

In the Modalist system, God manifests Himself, in the sense of reveals Himself, as the Father in creation, as the Son in redemption, and as the Holy Spirit in sanctification. There are not really three distinct persons in God but only three ways of considering God from the effects He has produced in the world.

Subordinationism
Unlike the foregoing, Subordinationism admits there are three persons in God but denies that the second and third persons are consubstantial with the Father. Therefore it denies their true divinity. There have been different forms of Subordinationism, and they are still very much alive, though not all easily recognizable as Trinitarian errors in which the mind tries to comprehend how one single infinitely perfect divine nature can be three distinct persons, each equally and completely God.

The Arians, named after the Alexandrian priest Arius, held that the Logos or Word of God does not exist from eternity. Consequently there could not have been a generation of the Son from the Father but only by the Father. The Son is a creature of the Father and to that extent a “son of God.” He came into existence from nothing, having been willed by the Father, although as “the first born of all creation,” the Son came into the world before anything else was created.

The Semi-Arians tried to avoid the extreme of saying that Christ was totally different from the Father by conceding that He was similar to or like the Father, hence the name Homoi-ousians, i.e., homoios = like = ousia = nature, by which they are technically called.

There was lastly the group of Macedonians, named after Bishop Macedonius (deposed in 360 AD), who extended the notion of subordination to the Holy Spirit, who was claimed not to be divine but a creature. They were willing to admit that the Holy Spirit was a ministering angel of God.

Tritheism 
At the other extreme to saying there was only one person in God was the heresy that held (and holds) there are really three gods. Certain names stand out.

According to John Philoponus (565 AD), nature and person are to be identified, or, in his language ousia = hypostasis. There are then three persons in God who are three individuals of the Godhead, just as we would speak of three human beings and say there are three individuals of the species man. Thus instead of admitting a numerical unity of the divine nature among the three persons in God, this theory postulates only a specific unity, i.e., one species but not one numerical existence.

In the theory of Roscelin (1120 AD), a Nominalist, only the individual is real. So the three persons in God are actually three separate realities. St. Anselm wrote extensively against this error.

Gilbert of Poitiers (1154 AD) said there is a real difference between God and the Divinity. As a result there would be a quaternity, i.e., three persons and the Godhead.

Abbot Joachim of Fiore (1202 AD) claimed that there is only a collective unity of the three persons in God, to form the kind of community we have among human beings, i.e., a gathering of like-minded persons joined together by their freedom to work together on a common enterprise. Joachim of Fiore is also known in doctrinal history as the one who projected the idea of three stages in Christian history. Stage One was the Age of the Father, through Old Testament times; Stage Two was the Age of the Second Person, the Son, which lasted from the time of the Incarnation to the Middle Ages; Stage Three began about the time of Abbot Joachim and will continue to the end of the world, as the Age of the Holy Spirit.

Anton Guenther (1873) was deeply infected with Hegelian pantheism and proclaimed a new Trinity. Guenther said that the Absolute freely determined Itself three successive times in an evolutionary process of development as thesis, antithesis, and synthesis. So the divine substance is trebled.

Post-Reformation Protestantism 
The original Reformers affirmed the Trinity without qualification. Thus Luther and Calvin, and the sixteenth century confessions of Protestant faith uniformly attested to the Trinity of Persons in God.
But the subjectivism of the Protestant principles paved the way to a gradual attrition of the faith, so that rationalism has made deep inroads into the denominations. The most common form of this rationalism takes the three persons in God as only three personifications of the divine attributes, e.g., divine power is personified by the Father, divine wisdom by the Son, and divine goodness by the Holy Spirit.

In this context, we may define rationalism as that system of thought that claims that the human mind cannot hold with certainty what it cannot understand. Since the Trinity cannot be fully understood, it cannot therefore be held to be certain.

Teaching of the Church
The history of the Church’s doctrine on the Trinity reaches back to the earliest days of Christianity. Our purpose here is to see in review some of the leading statements of the Magisterium, while pointing out some features of each document.

Pope St. Dionysius in 259 AD wrote a public letter to Bishop Dionysius of Alexandria in which he condemned the errors of Sabellius and the tritheist Marcion. The significance of this document lies in the fact that it paved the way for the Church’s later teaching, notably in the famous councils that dealt with the person of Christ. The popes led the way in defending the revealed mystery of the Trinity and in explaining its meaning, long before ecumenical councils entered the controversy. Even a few sentences from the pope’s letter will show the intransigence of the Church and her sureness of mind about the Trinity:

Sabellius’ blasphemy is that the Son is the Father, and the Father the Son. These men somehow teach there are three gods since they divine the sacred unity into three different hypostases completely separate from one another.

The teaching of the foolish Marcion who divides and separates the one God into three principles is a teaching from the devil, not the teaching of those who truly follow Christ and who are content with the teachings of the Savior.

At the Council of Nicea (325 AD), the Second Person was declared to be consubstantial with the Father, where the term homo-ousios became the consecrated word for expressing perfect numerical identity of nature between the Father and His Son who became incarnate.

But Nicea did not settle the controversy. Speculators, especially in the Near East, insisted on probing and rationalizing the Trinity so that in 382 AD Pope St. Damasus called a council at Rome in which he summarized the main errors up to his time. Called the Tome of Damasus, this collection of anathemas is a series of definitions on the Trinity that to this day are models of clarity. Twenty-four in number, a sample from the collection again reflects the Church’s perennial faith:

If anyone denies that the Father is eternal, that the Son is eternal, and that the Holy Spirit is eternal: he is a heretic.

If anyone says that the Son made flesh was not in heaven with the Father while He was on earth: he is a heretic.

If anyone denies that the Holy Spirit has all power and knows all things, and is everywhere, just as the Father and the Son: he is a heretic.

The most extensive declaration of the Church’s teaching on the Trinity was made at the Eleventh Synod of Toledo in Spain (675 AD). It is a mosaic of texts drawn from all the preceding doctrines of the Church. Its purpose was to assemble as complete a list of doctrinal statements as possible, in view of the still prevalent errors in nominally Christian circles, and (providentially) in view of the rise of Islam which struck with particular vehemence against the Iberian peninsula. Since the main target of Moslem opposition to Christianity was the Koranic claim that Christians were idolaters because they adored Christ as God, it is instructive to see how the faithful were prepared to resist the Moslem Unitarianism by a clear declaration of their own belief in the Triune God. The full text of doctrine at Toledo runs to over two thousand words. Only a few lines will be given to illustrate the tone:

We confess and we believe that the holy and indescribable Trinity, Father, Son, and Holy Spirit is one only God in His nature, a single substance, a single nature, a single majesty and power.

We acknowledge Trinity in the distinction of persons; we profess Unity because of the nature or substance. The three are one, as a nature, that is, not as person. Nevertheless, these three persons are not to be considered separable, since we believe that no one of them existed or at any time effected anything before the other, after the other, or without the other.

Two general councils of the Church formulated the faith in the Trinity in specific creeds, namely the Fourth Lateran and the Council of Florence.

The focus of Fourth Lateran was twofold, to reaffirm the faith in the face of the Albigensian heresy and to defend it against the vagaries of Abbot Joachim.

Since the Albigenses were Manichaens, for whom there were two ultimate sources of the universe, one a good principle and the other an evil one, Lateran declared the absolute oneness of God, who is at the same time Triune:

We firmly believe and profess without qualification that there is only one true God, eternal, immense, unchangeable, incomprehensible, omnipotent, and indescribable, the Father, the Son, and the Holy Spirit; three persons but one essence and a substance or nature that is wholly simple.

The Father is from no one; the Son is from the Father only; and the Holy Spirit is from both the Father and the Son equally. God has no beginning; He always is, and always will be. The Father is the progenitor, the Son is the begotten, the Holy Spirit is proceeding. They are all one substance, equally great, equally all-powerful, equally eternal. They are the one and only principle of all things—Creator of all things visible and invisible, spiritual and corporeal, who, by His almighty power, from the very beginning of time has created both orders of creatures in the same way out of nothing, the spiritual or angelic worlds and the corporeal or visible universe.

Abbot Joachim had a plurality of gods. In his effort to explain how the persons in the Trinity are distinct, he made them so separate that he ended up making them separate deities. Joachim’s problem was transferring what happens in human generation, when something of the parent goes over to the offspring, and is thereby distinct. He pressed the analogy too far and fell into error.

In response to this, the Fourth Lateran Council used the most technical language to insist that there is no division in God just because there is a distinction of persons:

The Father in eternally begetting the Son gave Him His own substance as the Son Himself testifies, “What my Father has given me is greater than all.” But it cannot be said that He gave Him part of His substance, and retained part for Himself, because the substance of the Father is indivisible, since it is altogether simple. Neither can one say that the Father transferred His own substance in generation to the Son, as though He gave it to the Son in such a way that He did not retain it for Himself; otherwise He would cease to be a substance.

The situation at the Council of Florence (1442 AD) was different. Here the need was to state the constant teaching of the Church with a view to reuniting the Eastern and Western Churches, separated by the Eastern Schism.

One feature of Florence, however, that needed to be clarified was brought about by the addition to the Nicene Creed of the expression Filioque, i.e. “and from the Son,” which Rome had approved. The Roman Creed now read, “the Holy Spirit, who proceeds from the Father and the Son.” The Easterners were uncomfortable with the addition, saying that Rome had tampered with a general council. The issue at stake was the true divinity of the Holy Spirit and the true divinity of the Second Person. Consequently, the Council of Florence, in the long Trinitarian Creed that it issued, stated as follows:

The Father is entirely in the Son and entirely in the Holy Spirit; the Son is entirely in the Father and entirely in the Holy Spirit; the Holy Spirit is entirely in the Father and entirely in the Son. None of the persons precedes any of the others in eternity, nor does any have greater immensity or greater power. From eternity, without beginning, the Son is from the Father; and from eternity and without beginning, the Holy Spirit has proceeded from the Father and the Son.

Human language could not be clearer, and there the faith of the Church stands to day and will until the end of time. Since the Council of Florence, popes and councils have simply drawn on the elaborate and absolutely unambiguous teaching of Sacred Tradition to offer the faithful for acceptance what is at once the glory of Catholic Christianity and its greatest revealed mystery.

Principal Implications
As we are learning today, faith in the Trinity is the basic test of our Catholic faith as Christians. This is not merely to say that objectively this doctrine is the most fundamental. It is. But subjectively, from our side, it is also the most crucial because it represents the hardest demand on our creedal assent.

All natural knowledge leads us to see only specific unity among human beings. We have one human nature, indeed, but we are only specifically one as distinct persons. We are really distinct as persons but we are also separate realities. Not so with the Trinity. Each of the divine Persons is the infinite God, and no one Person has only a “share” in the divine nature, a part of it so to speak. Yet they are not three infinities, but only one infinite God.

Relative to generation, all natural knowledge tells us that the parenthood and offspring imply a before and after generation, they imply a producer and a produced, a cause and effect. Not so in the eternal generation of the Son of God by the Father.

All natural knowledge tells us that while love is “outgoing” it does not literally give rise to a third person who is at once distinct from the two who love and numerically one with them in nature. Yet this is the case with God, where the Holy Spirit is declared by the Church as “the Love or the Sanctity of both the Father and the Son.” He proceeds from them without being another god.

But the Trinity is more than a test of our faith. It is also the perfect model of our selfless love. As revelation tells us, within the Godhead is a plurality of Persons, so that God is defined as Love because He has within His own being, to use our language, the object of love which is an Other with whom each of the Persons can share the totality of their being.

We therefore see from reflection on this Triune Love that love by its essence is not self-centered, that love unites, that love gives, and that love shares perfectly within the Godhead. Love is therefore as perfect in us as it approximates the perfect sharing that constitutes the Trinity.

At the same time, we recall that, while perfectly selfless in their mutual sharing of the divine nature, the Persons in the Trinity do not thereby cease to be themselves. Again, this is a lesson for us. We are to give of ourselves generously and without stinting. Nevertheless we are also to give in such a way that we remain ourselves and not become, as it were, something else in the process of sharing. There is such a thing as calculating charity, when a person gives of himself but “not too much” because he fears that his love may be too costly. This is not the teaching of Christ, who told us to love others not only as much as we love ourselves but as much as He loves us.

Saying this, however, is not to say that charity should not be wise. It would be unwise if it deprived us of that which God wants us to be and made us less than we are expected to be. Charity must, therefore, be enlightened; it must be guided by the standard of the Trinity, where each of the divine Persons gives and shares perfectly, yet without ceasing to be what each Person is to be. The Father does not become less the Father in begetting the Son and thus totally sharing the divine nature; nor do Father and Son cease to be themselves although they completely share their divinity with the Holy Spirit.

We thus have a confluence of two mysteries, of the Trinity in heaven and of liberty on earth. The Trinity is the pattern for our liberty. If we use our freedom to love others as we should, modeled on the Triune God, we shall reach that God in eternity. This is our hope, based on our faith, and conditioned by our love.

Father John Hardon, S.J., is founder of The Catholic Faith magazine.