A. There are three persons in the Godhead; the Father, the Son, and the Holy Ghost; and these three are one God, the same in substance, equal in power and glory.

By the word “Trinity” we mean one divine essence, three divine persons. This is what distinguishes the Christian idea of God from the other two monotheistic religions, Judaism and Islam. Even in the Old Testament, for the ancient Jews, while there were a collection of texts that bear witness to the triune nature of God, it is not until the New Testament that one can see the fullness of its revelation. 

Christian theologians have always been well aware that the word “Trinity” is not in the Bible. This is not a problem. Theology is done on the concept level. It is not the mere tracing out of verbal signs as an end in themselves. We might pause to consider that other words such as “monotheism” or “impute” or “biblical,” or “eternal state,” or any other number of terms that are suitable synonyms for ideas that all would agree are taught in the Scriptures, are not “in the Bible.”

Scripture and the Trinity

The doctrine of the Trinity has rightly been described as “progressively revealed” in the Bible. While the Old Testament does give us allusions of its truth, the relevant texts must be treated as pieces of a much larger puzzle, and as making sense mainly within the context of God’s promises to his covenant people. Without that appreciation for a building redemptive history, the majority of Old Testament texts will come across as random and forced. Having said that, we can consider three classes of texts that give different kinds of evidence. 

Naturally, Genesis 1:26, 3:22, and 11:7 are cited as instances of 1. a divine speaker 2. addressing the divine. That is to say, not only are words like “us” used, but attributes and actions are spoken of concerning the personal object of the personal subject’s speech which cannot be true of any being less than God. This is our first class of texts, those of first-person plural and second-person divine discourse. The same phenomenon is witnessed in Isaiah 6:8, “Then I heard the voice of the Lord, saying, "Whom shall I send, and who will go for us?" While Isaiah 54:5 is not inter-trinitarian speech, the word “Maker” is plural in Hebrew.

A second class of texts are those mysterious visitations, or appearances, from angels (angelophanies), most of which can also be shown to be a kind of “appearance” of Christ (Christophany) or more generally of God (theophany). Such texts include Genesis 12:7; 16:7-14; 18:1; 32:24, 28; Exodus 24:9-11; 33:11; Numbers 12:8; Deuteronomy 31:14-15; 34:1; Joshua 5:13-15; Judges 6:6-24; Isaiah 6:1-6; and Daniel 3:25. Which specific class each of these fit within is a subject that is not as simple to resolve as it may appear at first glance. Books II and III of Augustine’s classic On the Trinity is perhaps the most masterful treatment of this subject in church history, and by itself worth the price of the book. 

There is one last class of texts that round out our signs to the Trinity in the Old Testament. However, these are the passages that must be worked out in terms that theologians call “the economy of grace,” or in other words, that progressing history of redemption where God sends his Son, and then both Father and Son send the Spirit.

The obvious problem in proposing this to a Jew is that we are relying on much New Testament “background” that is really foreground. That is a legitimate method of interpretation if what we are doing is mere theology or else preaching. It is not a helpful approach in apologetics.

Having said that, Isaiah 43:10, Psalm 2:7, 110:1, and Micah 5:2 are passages of note in this class. If we ask for one verse where all three Persons are featured, the prophet Isaiah delivers: “And now the Lord God has sent me, and his Spirit” (48:16). Here it is the Son who speaks, but he speaks through the prophet.

All of this to arrive at the New Testament. There is a reason that the triune nature of God would be revealed more fully and all of a sudden here. This is the Incarnation of Christ and the outpouring the Spirit. And this is no mere addition of two actors onto the stage. We must consider what the Son and the Spirit do in salvation. With Christ, we have God with us—the Word made flesh (Jn. 1:14). With the Spirit, we have a renewed heart and with it an illumination of the deep things of God (1 Cor. 2:11-13).

Fred Sanders distinguishes between two basic ways to demonstrate the doctrine of the Trinity. Both are a kind of appeal to what the Bible shows us: one being an inductive approach and the other a deductive approach. The first we are hinting at here. That involves “entering more thoroughly into the meaning of Scripture.” Here the Trinitarian persons turn out to be everywhere because with new eyes we see what the Father, Son, and Spirit do. The second way is what Sanders calls a “piecemeal proof” where you “announce in advance the basic elements of the doctrine and then prove each of the various elements seriatim.”1

There are the familiar New Testament passages to which we commonly appeal. But the best approach is to divide these into a few categories.

Given the logic of the doctrine, we must first include all of the texts that show the deity of either the Son or the Holy Spirit (John 1:1-3, 18, 10:30; Acts 5:4, 9), and all of the texts that mention the divine Names in the same breath (Matthew 28:19-20; 2 Corinthians 13:14), and all that show subject-object distinction between the three Persons, whether there is speech between them, or a description of their works (Ephesians 1:3-14, 4:4-6).

Almost every word of John 14 through 17 falls into this category. 1 John 5:7 was used by the Westminster divines, and that because of its rendering in the King James Version. Since the use of that passage has its difficulties which would take us beyond this simple study, let us turn to the other text used by the Catechism: “Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit” (Mat. 28:19).

Logic and the Trinity

It is often asked, “How can all three Persons be one God, and each be different from each other?” In speaking of the Trinity, whether in Scriptural or later doctrinal formulations, there is a distinction to be made between 1. what is equal in the divine essence; and 2. what is proper to each of the three divine persons. When people raise the objection that the Trinity involves a logical contradiction, it becomes quickly evident that they misunderstand either the nature of logic or what the doctrine is claiming, or perhaps both. 

Cumulatively the Bible teaches that: (1) There is but one God; (2) All three of the Persons are referred to as God; (3) There is subject-object distinction between the Persons. If all three of these premises are sound, then the conclusion of One God in three Persons necessarily follows. 

Now, in order for any two or more terms to contradict (by the law of noncontradiction), we would need to show a genuine A and ~A. So, for instance, if the Trinity was “one gods and three gods” or “one person and three persons,” in either of those cases, we would have a real contradiction. However, this is a case of “one what, three whos.” One God, three Persons.

Church History and the Trinity

It will often be asked: When was this doctrine invented? The doctrine of the Trinity began the moment that its truth was revealed. Contrary to popular belief, while we may speak of doctrine as a product of church reflection, the truth of a doctrine is not reducible to a church “product.” A doctrine is either true or false, and the criteria for whether it is one or the other must be found on other grounds. The moment there is belief about any particular thing, there is a doctrine of that thing. But was it not codified by Councils? It was certainly more codified at Nicaea (325) and Constantinople (381), but the ways it was articulated were already being expressed by church fathers from the second century, and of course the relevant biblical passages constitute its doctrine.

The reason that there were such councils is not because of any fundamentally new idea. Rather, the church had to respond to a few errors about the nature of God that are still with us.

Those ideas can be roughly divided into three. At one extreme one can attempt to protect the unity of God at the expense of the revealed persons. Hence Modalism does this by explaining the persons as mere “modes” in which God’s existence has been manifested in time. He was the Father in the Old Testament, the Son during the incarnation, and the Holy Spirit starting at Pentecost. On the other extreme, one can press the three persons over against the one essence, making them three divine entities, or three essences, which we call Tritheism. 

Attempts were made to mediate between these. Arianism exalted the oneness of God, so that the Son was conceived of “similar substance” (homoiousios) to the Father, rather than the “same substance” (homoousios). As Arius was reputed to have said about the Son, “There was when he was not.” Adoptionism held that the Son became divine by virtue of being made the Son of God at his baptism, which was the first point in the temporal narrative that this was said about Jesus. None of these positions did justice to all that the Scriptures taught. None of these could explain why Christ and the Holy Spirit were to be worshiped, and how the Persons could refer to each other as having what is proper to distinct persons.

Theology Proper and the Trinity

Our Catechism answer ends with the qualification: the same in substance, equal in power and glory. How can the three Persons be spoken of as they are—as if existing in particular modes and doing things that seem to imply greater and lesser levels of glory or being? Part of the answer—especially in texts like 1 Corinthians 11:2 or 15:28 about Christ being subordinated to the Father—is that the Son is often spoken of not only in the economy of works, but also as to his human nature. It is in this sense that the Father is the head of Christ, or that the Son presents the kingdom to the Father. 

But there is a more general slowness of our minds to keep track of what is one in essence and what is proper to the Persons. Brakel is helpful here. He begins with Hebrews 1:3, where the Greek word hypostasis is used of Christ—namely, of a person being the Image of another person—and speaks of all such Trinitarian language as if anthropomorphisms to help us understand something, at least, that would be otherwise incomprehensible. In Hebrews 1:3, the Son is being considered in “an abstract sense” whereas in Philippians 2:6, he is being considered in “a concrete sense.” Brakel does not mean “abstract” in an immaterial sense, and “concrete” in a material sense.2 

Rather, to “consider one of the divine Persons in an abstract sense” is to speak of them as if “outside of the context of the divine Being,” which literally and ontologically speaking they never are. Yet the Scripture itself does this to “press pause” on our mind’s otherwise impossible connection to the God of simple and pure act. And why? The same reason behind any other anthropomorphism: to show us one true thing without our minds exploding around the weight of infinite glory.

Now by contrast, to consider one of the divine attributes in the “concrete” is, Brakel says, is “viewed in union with the divine Being.”3 So for Paul to say that Jesus was “in the form of God” (Phi. 2:6) is to assign a predicate of what is shared in the essence and no longer what is proper to the Person. What is proper to each Person is incommunicable, such that the Father is in no sense the Son, and vice versa; nor is the Spirit in any sense the Father or the Son, and vice versa.  

Is the Trinity an essential doctrine? Think of it this way — If we take away our knowledge of the Trinity, then the biblical worldview would collapse and there would be no gospel. In other words, objectively speaking, the Trinity is absolutely essential to the Christian faith. Things get one notch trickier when viewing this from a subjective point of view. In other words, supposing we ask it this way: Is belief in the Trinity essential to one’s own salvation? The answer is that it depends on what is meant by “belief.”

If we are talking about a profound understanding of the mystery of the Trinity, well, then no, for that would be to make our intellectual performance a kind of meritorious work. And besides, no Christian has accomplished more than scratching the surface of its mystery. On the other hand, if what we are talking about is someone who sees what the doctrine means and turns away in disgust or pride, then this is entirely another matter. And this is the position that one who calls themselves a Unitarian or a Modalist has really put themselves in. These are not simple Christians who are making their first attempts to express what they see in Scripture. These are those who say, “We see,” and thus their error is also sin. 

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1. Fred Sanders, The Triune God (Grand Rapids: Zondervan, 2016), 172.

2. Brakel, The Christian’s Reasonable Service, I:141.

3. Brakel, The Christian’s Reasonable Service, I:141.