An Introduction to the Trinity

Unity and Distinction in God


As we move from the attributes of God, we come to a profound ineffability in Christian theology: the unity and distinction of persons in the Godhead. In a recent series, we covered one aspect of God: “The Attributes of God.” Now, we speak of his triunity. God truly is one God of unity, especially declared so in the doctrine of divine simplicity. Yet, this one simple God, who is in and of himself, is who he is in three distinct persons: Father, Son, and Spirit. With this notion, we come to the foundation and ruler of all Christian theology—the Holy Trinity.

The Holy Trinity is not simply a doctrine amongst others in Christian dogmatics, nor is it merely an important doctrine; rather, it is pervasive and foundational.[1] It determines how all other doctrines are. When we think of the Holy Trinity, our minds often think of the economic Trinity (God acting in creation), but in this article and those to follow, we primarily consider the immanent or ontological Trinity, that is, God as he is in himself as Father, Son, and Spirit.

A  Great and Difficult Doctrine: Dangerous, but Profitable

We would do well to agree with Augustine’s note on studying the Trinity: “in no other subject is error more dangerous, or inquiry more laborious, or the discovery of truth more profitable.”[2] To comprehensivley define the immanent Trinity is impossible and reductionistic, for God is infinitely transcendent and we are fallen, finite creatures. Human reason will never penetrate this blessed Trinity in its all-glorious, tripersonal, undivided essence. The doctrine of the Trinity is the first of the most difficult topics that Christian theology attempts to understand. In this regard, Francis Turretin says, “In the Christian religion there are two questions above all others which are difficult. The first concerns the unity of the three persons in the one essence in the Trinity” (the second being the two natures of Christ).[3] 

But Take Heart

After hearing how difficult this doctrine is, many will turn out of fear, laziness, and whatnot. But take heart. My first time teaching on the Trinity, I opened with a word from 1 Corinthians 2:6–15, which may not necessarily be on trinitarian doctrine, but I think it’s helpful and hopeful when approaching such a daunting topic. One out of a few principles I think we can take from this text is that by divine revelation and the Spirit’s working, we really can know who God is because we have the indwelling, Holy Spirit who “searches everything, even the depths of God” (1 Cor 2:10). Therefore, we really can study, think about, and know deep things of God because “we have the mind of Christ” (2:16). So take heart, God has revealed himself in the Scriptures and his Holy Spirit illumines the eyes of man to see him for who he is.

Two Heretical Ditches: Sabellianism and Tritheism

In the attempt to answer the question of how God is one God in three distinct persons, many have commonly used this ectypal (incomplete and finite) expression: “three-in-one.” The three-in-one being is truly an incomprehensible mystery. This seeming paradox, “three-in-one,” has caused many to have faulty understanding of God’s unity and tripersonal nature. Two reoccurring heresies that refer to the general sense of oneness or plurality of God include Sabellianism and Tritheism, which both consequently lead to other heresies. The former rejects essential, personal distinctions and the latter rejects essential unity.


Sabellianism (often called Modalism), founded by the 3rd century Roman presbyter Sabellius,[4] is the ancient belief “that there is one God who can be designated by three different names—‘Father,’ ‘Son,’ and ‘Holy Spirit’—at different times, but theses three are not distinct persons.”[5] In other words, according to Sabellianism, the one God is not three persons; rather, the one God is one person who reveals himself throughout history in three different characteristic manners: as Father, as Son, and as Spirit.[6] Thus, in the attempt to maintain the unity of God in light of the three persons, Sabellianism “denies the ‘threeness’ present in the divine being [and] … seeks to secure the oneness, not by placing the Son and the Spirit outside the divine being, but by so absorbing them into it that all distinctions among the three persons melt away.”[7] Hence, to say it again, Sabellianism rejects the real, essential plurality of the persons and instead views the persons as “character masks” of God in order to maintain his unity. This heresy, then, implies distinct manners of God that only exist in our understanding or perception of God. Thomas Aquinas puts it this way: “If no real paternity [fatherhood] or filiation [sonship] existed in God, it would follow that God is not really Father or Son, but only in our manner of understanding; and this is the Sabellian heresy.”[8] Whereas Sabellianism rejects the distinct persons of God, far on the other side of the spectrum, Tritheism emphasizes plurality and rejects unity.


Tritheism is the belief that “God is three persons, with no unity of essence.”[9] Consequently, Tritheism believes that there are three gods, which means that Tritheism is polytheism—the belief of multiple gods (similar to many ancient, pagan beliefs).[10] According to Wayne Grudem, a Tritheist’s logic is this: “God is three persons and each person is fully God. Therefore, there are three Gods.”[11] Thus, Tritheism ultimately denies that there is only one God. It must be noted, however, that this view of the Trinity is uncommon and “Few persons have held this view in the history of the church,” and further, “no modern groups advocate Tritheism, perhaps many evangelicals today unintentionally tend toward tritheistic views of the Trinity, recognizing the distinct [persons] … but seldom being aware of the unity of God as one undivided being.”[12]

Unity and Distinction Not at Odds

In laying out these misunderstandings of the Trinity, it seems to be that there are “two ditches” of faulty conclusions regarding the unity and tripersonality of God: rejection of the distinction of persons and rejection of the unity of persons. 

In God, threeness does not pit against oneness or vice versa. Thus, we ought not think that distinction and unity are at odds, nor should we separate them and hold one over the other. John Webster puts it this way:

 Applied to God, “one” and “three” are mutually interpretive and reinforcing. God’s unity is not tout court but triunity; God’s threeness is the threeness of the persons of the one indivisible divine essence. Threeness is not something additional to oneness; oneness is not a combination of three or divisible into three.[13]

So, how then should we speak of the triune God?


In the following posts, we wish to offer a biblical understanding of the Trinity and thus refute both Tritheism and Sabellianism to show that God is triune as he is triune and that unity and distinction are not at odds in God. Our hope is to show that God really is three distinct persons, Father, Son, and Spirit, and that God really is one even in these personal distinctions. However, in doing so, especially when we focus on the distinct persons of Son and Spirit, we will necessarily have to face two other heresies: Arianism and Pneumatomachianism.

 Arianism, which will further be expounded in another article, is the denial of the eternal equality and divinity (consubstantiality) of the Son with reference to the Father. Pneumatomachianism, which will be further discussed in another article, is the rejection of the eternal equality and divinity (consubstantiality) of the Spirit with reference to the Father (and Son). In our attempt to expound the unity and tripersonality of God, our hope is to maintain both unity and distinction while arguing for the equality of the three divine persons.

Here’s a brief statement of what the following articles in the systematic theology category will expound: God is one in three distinct persons. These distinct persons are God the Father, God the Son, and God the Spirit. Each person is in equal to the other two—there is no ontological (essence) inferiority or superiority or priority between the persons. They are so equal that they are identical in essence (homoousios; consubstantial) and so, each person can only be distinguished by relation of origin (divine processions), that is, by the way they relate to the other divine persons. Hence, the persons all subsist in the undivided, divine essence, which indicates their consubstantiality (unity and equality), and they also have their own personal properties marked out by how they relate to each other, which shows that one is not one of other two (i.e., to show that they are distinct persons). Oneness does not trump threeness, and threeness does not trump oneness.

Here’s the tentative schedule for the following posts in the Systematic Theology Category:

1. Distinctions of Divine Persons

2. The First Person of the Trinity: God the Father

3. The Second Person of the Trinity: God the Son

4. The Third Person of the Trinity: God the Spirit

5. How Unity and Distinction Are Not at Odds in God

Note: Feel free to email for further questions, clarifications, or suggestions in any of these Trinity articles, as they are indeed covering a very difficult topic.


[1] Hence, John Webster, God without Measure: Working Papers in Christian Theology vol. I God and the Works of God (London: Bloomsbury T&T Clark, 2016), 1:159–175.

[2] Augustine, De Trinitate, I.3.5.

[3] Francis Turretin, Institutes of Elenctic Theology, 2:310.

[4] Michael Horton, The Christian Faith: A Systematic Theology for Pilgrims on the Way (Grand Rapids: Zondervan, 2011), 279. This is also called “modalism,” but due to the language we will use about speaking of the divine persons, we will continue to call it Sabellianism for the sake of clarity.

[5] Gregg R. Allison, Historical Theology: An Introduction to Christian Theology (Grand Rapids: Zondervan, 2011), 235.

[6] Horton, The Christian Faith, 279–280, 997.

[7] Herman Bavinck, Reformed Dogmatics ed. John Bolt, trans. John Vriend (Grand Rapids: Baker Academic, 2003–2008), 2:292.

[8] Thomas Aquinas, Summa, 1a.28.1 sed contra. Emphasis added.

[9] Horton, The Christian Faith, 279.

[10] Wayne Grudem, Systematic Theology: An Introduction to Biblical Doctrine (Grand Rapids: Zondervan, 1994), 248.

[11] Ibid., 247.

[12] Ibid., 248.

[13] John Webster, God Without Measure, 1:87, and Webster further says, 

“As we consider the relation of the common divine essence and the three divine persons, we ought not to allow ourselves to be mesmerized by the contiguous but nevertheless rather different distinction between Deus unus and Deus trinus, especially when the latter distinction is taken (as it is by some contemporary trinitarians) to indicate the irreconcilability of generic (mono)theism and a doctrine of God emphasizing personal differentiation. As it is usually deployed, the distinction between the one God and the triune God already opposes what the concept of God’s indivisibility seeks to hold together, namely, “essentialism” and “personalism.” Avoiding the opposition requires that we do not settle either on a conception of the one divine essence in isolation from the three persons, or on a conception of the three persons in isolation from the one divine essence; and it further requires that we avoid thinking of unity and threeness as serially related, and that we do not confuse essential and relative predication. These stipulations, easy to state, prove remarkably taxing to follow” (ibid., 86–87).