There is never a point in the New Testament when Paul writes to a church, “Now concerning the three persons in the one God, brethren, I would not have you ignorant.” That doesn’t happen because neither Paul nor the other apostles ever announce to the church for the first time that we have received information that God is triune. The churches exist because the Son and the Spirit were sent on the mission of the Father. The kind of work that Paul and the apostles are doing is alluding to a revelation that they had already received.

To contemplate the Trinity is to lift up your heart and to “set your mind on the things above” (Col. 3:2).

It’s easy to turn doctrinal discussions into strictly intellectual affairs, but as Dr. Fred Sanders teaches in The Triune God course, we need to do so “in a way that enlists the reader’s strict and holy attention for what is essentially a spiritual exercise.”

Any discussion of trinitarian doctrine is an attempt to more deeply understand the character and nature of God.

If we’re interested in discovering (and maintaining) an orthodox understanding of the Trinity, there are some principles we need to understand.

These 11 things you need to know about the doctrine of the Trinity are adapted from his course:

1. THE REVELATION OF THE TRINITY COMES WITH THE REVELATION OF THE GOSPEL.

The doctrine of the Trinity is need-to-know information that we didn’t need to know with any clarity until, as Paul puts it:

“When the set time had fully come, God sent his Son, born of a woman, born under the law, to redeem those under the law, that we might receive adoption to sonship. Because you are his sons, God sent the Spirit of his Son into our hearts, the Spirit who calls out, ‘Abba, Father.’”
—Galatians 4:4–6

God published both the revelation of the gospel and the revelation of the Trinity same time, in the same ways: more obscurely and by way of anticipation under the old covenant, more luminously and by way of fulfillment under the new.

The question of whether the Trinity is revealed in the Old Testament runs parallel to the question of whether the Gospel was.

In both cases, Trinity and gospel, we must account for two factors:

1. The consistency of God’s entire work of salvation

2. The newness in “the revelation of the mystery that was kept secret for long ages” (Rom. 16:25) “which was not made known to the sons of men in other generations as it has now been revealed . . .” (Eph. 3:5).

2. THE REVELATION OF THE TRINITY ACCOMPANIES SALVATION.

We make statements in the doctrine of the Trinity that would be true of God even if we didn’t exist or if the incarnation had never occurred. But what we know about the Trinity always accompanies salvation, and always flourishes in the context of teaching about salvation. This is why the doctrine of the Trinity has been the quintessential catechising doctrine throughout church history.

Even though it can be stated propositionally and in the form of information, the doctrine of the Trinity was not given primarily as information. Rather, this knowledge came along with the carrying out of God’s work of salvation.

God saves, and further, wants the saved to “understand the things freely given us by God” (1 Cor. 2:12). God did not hand down statements regarding the Trinity, but extended his arm to save, an action that by design brought with it knowledge of the one doing the saving.

As B. B. Warfield wrote, “The revelation of the Trinity was incidental to, and the inevitable effect of, the accomplishment of redemption.” (B. B. Warfield, “The Biblical Doctrine of the Trinity,” in Biblical and Theological Studies)

The doctrine of the Trinity is not mainly for apologetics or for opposing heretics (although that’s been an important element of the doctrine); it’s mainly for the purpose of teaching Christians what they believe about God on the basis of being saved by that God.

3. THE REVELATION OF THE TRINITY IS REVELATION OF GOD’S OWN HEART.

It’s hard not to use more emotional language here. As Thomas Goodwin, says, “The gospel reveals the deep things of God.”

When God makes himself known to us and saves us, what he reveals is something from the fundamental depths of who he is.

Theology, broadly considered, is knowledge of God and of all things in God; “all things” are accounted for by a great many doctrines. But the doctrine of the Trinity is theology proper—the knowledge of God.

Its focus is not on those aspects of the divine nature that are knowable by the things created or of God in relation to things outside of him; those things are spoken of in Scripture substance-wise, according to God’s one nature. But the doctrine of the Trinity is a statement about God’s interior life, requiring statements relation-wise, internal to the divine being, describing the Father and the Son and the Spirit as they stand toward each other.

Prepositions will be decisive here: “That true and absolute and perfect doctrine, which forms our faith, is the confession of God from God and God in God” (Hilary of Poitiers, On the Trinity).

If we’re able to say that the Holy Spirit is God or that Jesus is God, we’re able to say that what is made known to us in the Son and the Spirit is about the very heart of God.

4. THE REVELATION OF THE TRINITY MUST BE SELF-REVELATION.

The way that God made himself known was not declarative. He didn’t tell us, “I am Father, Son, and Spirit.” He actually sent the Son and the Spirit so that they were here among us, revealing themselves by making themselves present.

This knowledge cannot be delegated or delivered by proxy. As Hilary of Poitiers said, “Since then we are to discourse of the things of God, let us assume that God has full knowledge of Himself, and bow with humble reverence to His words. For He Whom we can only know through His own utterances is the fitting witness concerning Himself” (On the Trinity).

5. THE REVELATION OF THE TRINITY CAME WHEN THE SON AND THE SPIRIT CAME IN PERSON.

As was said in the last point, the doctrine of the Trinity wasn’t shouted over the ramparts of heaven. “But when the fullness of time had come, God sent forth his Son . . . And because you are sons, God has sent the Spirit of his Son into our hearts, crying ‘Abba! Father!’” (Gal. 4:4, 6).

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