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Unlike the canon of Holy Scripture, which is completely outside of Holy Scripture, all of the other doctrines upheld and defended by the Church were hinted at, or implicitly contained, in Holy Scripture but not explicitly stated. Because they were not explicitly stated for public belief, they have often become the occasion for the rise of heresies in the Church. Thanks to her Sacred Tradition, the Church found a way to elucidate and define these dogmas and beliefs, preventing it from plunging into error.

Again, this might be a surprise to many, but the mystery of the Blessed Trinity—that there are three Persons in one God—is one of those fundamental doctrines that are not clearly stated in the Holy Scripture. Of course, Christ hinted at the doctrine when He said, "Going, therefore, teach ye all nations; baptizing them in the name of the Father, and of the Son, and of the Holy Ghost" (Matt 28:19). But that still does not say clearly that these three—the Father, the Son, and the Holy Spirit—are three Persons in one God. In fact, the word "person" is not in the Holy Scripture.


Historical Development of the Doctrine of the Trinity


The Bible clearly states that there is one God (Deut 6:4; 1 Par 17:20; Mark 12:29).  It also says that the Father is God (Mal 2:10; Luke 10:21; 1 Cor 8:6). It teaches that the Son, Jesus Christ, is God (John 1:1; Col 2:8–10; Titus 2:11–14) and that the Holy Spirit is God (Acts 5:1–4; 1 Cor 3:16). But how can all three—the Father, the Son, and the Holy Spirit—be God when there is only one God? That is the problem. The word "person," as distinguished from substance or nature, was not used until the third century. The precise formulation of the doctrine of the Trinity, which avoids the apparent contradiction, was missing in Holy Scripture.

As a result of the lack of precise statements describing the dogma of the Blessed Trinity in Holy Scripture, the following heresies developed during the first three centuries of the Christian era:


  • Tri-theism held that the Father, the Son, and the Holy Spirit were three different Gods.

  • Sabellianism taught that the Father, the Son, and the Holy Spirit were three modes or aspects of the same God and, therefore, not distinct from one another.  

  • Subordinationism, which taught that the Son and the Holy Spirit were subordinate to the Father and therefore not equal to Him in being and perfection.

But faith in the Trinity has always existed in Sacred Tradition! The above-mentioned heresies were called "heresies" because they were opposed to what the Church believed: 


  • In contrast to Tritheism the Church believed that God was one.

  • Against Sabellianism the Church believed that the Father, the Son, and the Holy Spirit were really distinct from each other, such that the one who was born of the Virgin Mary was only the Son, not the Father nor the Holy Spirit, and that the one who descended at one time as a dove (at Christ's baptism), at another time as a cloud (at the Transfiguration), or as tongues of fire (at Pentecost) was the Holy Spirit, not the Father nor the Son.

  • Against Subordinationism, the Church believed that, although each was different from the other, the Father, the Son, and the Holy Spirit were all equal in divinity, power, and perfection.


Despite the lack of appropriate vocabulary to make a precise formulation of the doctrine, the Church kept and preserved the faith in the Trinity handed on by Christ and the Apostles during the first years of Christianity. For example, see how the good St. Irenaeus of Lyons (A.D. 125–200) proclaimed the faith of the Church:

"The Church, though dispersed throughout the whole world, even to the ends of the earth, has received from the apostles and their disciples this faith: [She believes] in one God, the Father Almighty, Maker of heaven, and earth, and the sea, and all things that are in them; and in one Christ Jesus, the Son of God, who became incarnate for our salvation; and in the Holy Spirit, who proclaimed through the prophets the dispensations of God ..." Against Heresies, Book I, Ch. 10, par. 1.


The first use of the word "Trinity" was in A.D. 180, when the ecclesiastical writer Theophilus of Antioch, in his Apology to Autolycus, Book II, Ch. XV, spoke of the Trinity "of God, and His Word, and His wisdom." Then, a few decades later, another ecclesiastical writer, Tertullian (A.D. 155–225), in his book Against Praxeas, designated the Father, the Son, and the Holy Spirit as "persons" of the one Divine Substance. Although his theories regarding the "material" constitution of the Divine Substance and the procession of the Divine Persons were flawed, his distinction between "person" and "substance" or "nature" paved the way for a more precise formulation of the doctrine of the Trinity.

By the time St. Gregory Thaumaturgus (A.D. 213–270) wrote his thoughts on the Trinity, the vocabulary was already available to state the doctrine of the Trinity more precisely. The following quotes are from his A Sectional Confession of the Faith (SCF):


"That there are indeed three persons, inasmuch as there is one person of God the Father, and one of the Lord the Son, and one of the Holy Spirit; and yet that there is but one divinity, inasmuch as the Son is the Image of God the Father, who is One — that is, He is God of God; and in like manner the Spirit is called the Spirit of God, and that, too, of nature according to the very substance, and not according to simple participation of God."  SCF #14

"We acknowledge that the Son and the Spirit are consubstantial with the Father, and that the substance of the Trinity is one — that is, that there is one divinity according to nature, the Father remaining unbegotten, and the Son being begotten of the Father in a true generation, and not in a formation by will, and the Spirit being sent forth eternally from the substance of the Father through the Son, with power to sanctify the whole creation." SCF #18 (Italics added)​​

St. Gregory Thaumaturgus

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At the First General Council of Nicea, A.D. 325, the same terminology was used in the Profession of Faith of the 318 Fathers. Then at the First General Council of Constantinople, A.D. 381, in the Exposition of the 150 Fathers, a statement expressing belief in the Blessed Trinity formally became part of the Creed.

Description of the Blessed Trinity During the Middle Ages

The medieval theologians, particularly St. Thomas Aquinas (in his Summa Theologiae, Part I, Q. 27–43), refined the philosophical concepts of "nature," "substance," "person," etc., and these became the Church's tool for describing the mystery of the Blessed Trinity. Today, the Church still uses the word "substance" or "nature" to designate the divine being in its simple unity, while She uses the word "person" to designate the Father, the Son, and the Holy Spirit in their different relations within the Godhead. To better understand the thoughts of the medieval theologians on the Trinity, it would be helpful for the reader to be acquainted with some of the terminologies they were using, such as "substance" and "accidents," "essence" and "existence," etc. For a quick review of these concepts and terminologies, click the button below.

  • Among creatures, there is a distinction between a substance and its accidents, because accidents are determining features of a substance. A man is distinct from his wisdom, which, as an accident, cannot exist except in himself as its subject. But in God, in whom there are no accidents, it is proper to say not merely that God is wise but that He is Wisdom itself, because there is no distinction between His substance and His wisdom. Thus, God is the same as Subsistent Wisdom. The same is true of the relationships within the Godhead. Among creatures, relations are accidents of their substances; my fatherhood exists in me but is not my substance. But in God, the relations are God Himself. Hence they are called "Subsistent Relations" (ST, Part I, Q. 29, art. 4). The Father, as Father to the Son, is God. The Son, as the image of the Father and eternally begotten from the Father, is God. The Holy Spirit, as the love between the Father and the Son, and proceeding eternally from both, is God. These relations are "consubstantial" and do not really differ from each other with respect to the Divine Substance.

  • Although God is one substance, the Father, the Son, and the Holy Spirit are not simply modalities of the divine being, as the Sabellians believed, because they also differ in terms of their relationships. The Father is distinct from the Son as the one generating. The Son is distinct from the Father as the one begotten. The Holy Spirit is distinct from the Father and the Son as the one who proceeds from both. So, while all these Relations are the same with respect to the divine Substance, they are really different with respect to each other as opposite terms of their relations (See ST, Part III, Q. 39, art.1.) There is no internal contradiction here, for it is not impossible for two or more things to be the same in one respect but different in another.

  • A man can have several distinct relationships within himself. For example, a man can be a father to his son, a son to his father, a teacher to his pupil, and a pupil to his mentor. But in man, these relations are mere accidents of, and not identical with, his substance. These relations exist in him but are not identical to his essence. In God, in whom there are no accidents, the three relations—Father, Son, and Holy Spirit—are identical to the Divine Substance, which is why each relation is the same God. But, just as in creatures, there can be several accidental relations in one created subject, so in God, in whom relations are identical to the Substance, it is not impossible to have a Father, Son, and Holy Spirit, which are different with respect to each other as opposite terms of their relations but which are the same with respect to the Divine Substance.

  • But how do we know that the Father, the Son, and the Holy Spirit are Subsistent Relations within the Godhead? We cannot find this out by reason alone. It was revealed to us in Holy Scripture. In many instances, Holy Scripture spoke of the Father, the Son, and the Holy Spirit. We cannot demonstrate the existence of these relationships within one God solely through reason. However, we can find reasons why this is true after the fact—that is, after it was revealed to us as a fact. Because the Father is an intelligent Substance, His first act is to know Himself. His knowledge of Himself, or the image He forms of Himself, is the Word (God the Son), which again is not an accident but a Relation that subsists in the Divine Substance. The Father and the Son love each other eternally, which is how the Holy Spirit—the Subsistent Love between the Father and the Son—proceeds from both (ST, Part III, Q. 28, art. 4).

  • In the theology of the Trinity, the Divine Relations are called "Persons" because, by definition, a person is an intelligent substance responsible for its act. Since the Divine Relations are identical to God's Substance, which is an intelligent substance, they are each responsible for their acts. In other words, each Subsistent Relation is a Divine Person. The act of one Person is His act alone, not the act of another. Thus, the Father is the One sending, while the Son is the One sent and the one who alone took our human nature, suffered on the Cross, and redeemed us from sin. The Son alone, and not the Father, is our Redeemer. Similarly, the Holy Spirit is the Person sent by both the Father and the Son and is the One who alone justifies and sanctifies.

  • Realizing that each Person of the Blessed Trinity has an act distinct from that of another Person, it is also correct to say that only the Son was born of the Virgin Mary, not the Father nor the Holy Spirit. And only the Holy Spirit descended as a dove, not the Father nor the Son. The Father, the Son, and the Holy Spirit are three different Persons with different personal acts and missions. But they are all equal in dignity, power, and perfection because they are all identical to the same Divine Substance.

  • Although the three Divine Persons have different acts with respect to generation (generating, being begotten, or proceeding) or their mission (sending or being sent), they all work together in unison in all the works of God where the Divine Substance is the principle of operation, such as in the creation and governance of the world, the exercise of Divine Power, etc. Likewise, although only the Son of God took human nature during the Incarnation, all three Persons worked to unite human nature with the Son (ST, Part III, Q. 3, Art. 4). In the same manner, although the Holy Spirit is the Person who alone justifies, it is the tri-personal God, the entire Trinity, and not only the Holy Spirit, who dwells in the souls of the just. 

  • In spite of the fine-tuning made by St. Thomas to the meaning and use of the words "person," "relation," and "substance," the existence of three distinct Persons in one God is still a profound mystery and difficult to grasp. It is difficult to understand how different Persons could be identical to the same Divine Substance and still remain distinct, as Persons. But that is, in fact, the case, which is why we say that the Blessed Trinity is a mystery. It is above reason, yet it is not against reason because it is not impossible.

The Church repeated the same teaching in the Catechism of the Catholic Church, # 232–260.

Holy Trinity Statue

On top of the Holy Trinity Column in Olomouc, the Czech Republic

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The Filioque Clause

The Creed of the Council of Constantinople said that the Holy Spirit proceeded "from the Father," but later editions of the Creed in the Latin rite said that the Holy Spirit proceeded "from the Father and the Son (filioque)." This is the so-called filioque clause that has become, and still is, the subject of contention between the Greek Orthodox Church and the Roman Catholic Church. How the filioque clause crept into the Creed is a subject of speculation but it could have been done as early as A.D. 410 in the local Council of Seleucia-Ctesiphon. Anyway, leaders of the Greek Orthodox Church objected that the filioque addition was inappropriate because the Holy Spirit proceeded from the Father through the Son, not from the Father and the Son. However, the Latin Rite leaders of the Roman Catholic Church found nothing wrong with the added clause.

The Greek Orthodox Church views the filioque clause as a departure from the faith of Nicea and Constantinople. They feel that the phrase "from the Father and the Son" implies that something is being received from the Son that is not from the Father, whereas the phrase "from the Father through the Son" implies that everything is coming from the Father through the Son. On the other hand, the Catholic Church thinks that it is safe to say that the Holy Spirit proceeds from the Father and the Son because everything the Son has is also from the Father anyway, so everything is still coming from the Father as the ultimate source. Although there are other issues that divide the Greek Orthodox and Roman Catholic Churches, it appears that the filioque issue is more about semantics than doctrinal differences. The two phrases are actually both correct and have both been employed by many of the Church Fathers when talking about the procession of the Holy Spirit.


As shown in the above discussions, the doctrine of the Trinity has always existed in Sacred Tradition. Thanks to Her Sacred Tradition the Church managed to resist the heresies that threatened to corrupt the faith in the first centuries of Christianity. The teaching of the Trinity never changed, but the language in which it was expressed got better with time. Today, we have the concepts and technical vocabulary needed to state the doctrine precisely. We owe this to the skill of medieval theologians who refined the concepts and terminology with their faith and philosophical acumen. Even if the language and concepts had improved, it would have had no effect if Sacred Tradition had not been present to capitalize on it. We, therefore, equally owe our present understanding and formulation of the doctrine of the Blessed Trinity to Sacred Tradition.

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