What do you think of when you hear the word "Trinity"? Do you think of eggs, or clovers, or the three states of water? If you do, you have a sub-biblical, at best, and unorthodox, at worst, understanding of God.

What's the big deal?  We must understand God as he has revealed himself. It affects our understanding of God in general and affects our interpretation of his works in creation and our salvation. If we get this wrong, then the God we preach will not be the God of the Bible. At best, it will be a distorted facsimile. 

The Trinity is central to the Christian life and its evolution. Fred Sanders writing for Crossway's Ten Things You Should Know series, states, "Whether you have been attending to it or not, everything about the Christian life works only because there is a Trinitarian reality underlying it. If you got saved, you got picked up by the Trinity and brought into God's own fellowship. Learning about the Trinity is a matter of learning the deeper reasons why this Christian life works." 

Sanders and Oliver D. Crisp further stress the importance of the Trinity in the Christian's life in his chapter in Advancing Trinitarian Theology: Explorations in Constructive Dogmatics, "First, Trinitarian theology summarizes the biblical story. Second, it articulates the content of divine self-revelation by specifying what has been revealed. Third, it orders doctrinal discourse. Fourth, it identifies God by the gospel. And fifth, it informs and norms soteriology."

The summary of the Bible. In the opening pages of Scripture, God promises that he would send the one who would crush the serpent. This promised salvation is repeated to Abraham, Judah, King David, Israel through the prophets and is fulfilled in the Incarnation, Jesus' baptism, the sending of the Holy Spirit.

At the baptism accounts, Scripture gives us a glimpse of the cooperative activity of the Trinity. The Father, Son, and Holy Spirit revealing to John the observers at the Jordan river and us today, the Father's plan of salvation unfolding. 

There also allusions to the Trinity in the Old Testament. Space constraints prevent us from discussing them here, but Zondervan has an excellent overview.

Articulating God's self-revelation.  God is eternal, not bound by space or time. We are finite, bound by space and time. In The Forgotten Trinity, James White writes, "We struggle with God's eternity ... our lives are conditioned by the passing of time." God has always been, and his revelation to us as Father, Son, and Spirit is part and parcel of saving his people. 

Doctrinal discourse. The Trinity informs our theology and doctrine. When we say that Jesus is divine or the Son of God, we make what theologians call Christological claims. To paraphrase Sanders, all theology is about God primarily, and secondarily about all other things in relation to God; thus, it is critical to our understanding of God and everything else. 

God and the Gospel. It is the Triune God that saves. 

• Ephesians 1:3–6 tells us that salvation originates with the Father.

• Ephesians 1:7-12 explains that salvation is brought to fruition in the Son.

• Ephesians 1:13–14 tells us that the Holy Spirit communicates salvation.

The doctrine of the Trinity connects the eternal God of creation to his acts in history, leading to the salvation of his people. 

Isn't the Trinity beyond human comprehension? No. And, yes. The Church's confession of the "mystery" of God's triune nature should be understood as claiming that it transcends our rational comprehension, not that it violates logic or makes a nonsensical claim. The "mystery" is also theological (or biblical) in the sense that it is revealed over time. God has always been triune, but this fact is revealed in the Incarnation of Jesus Christ

John Calvin wrote that when we abandon trinitarian theology, we are left only a "bare and empty name of God [that] flits about in our brains, to the exclusion of the true God." It is that important. We all have a theology; we must make sure we have a sound theology (Colossians 2:8).

Thankfully, we are not left in the dark as to the nature of God. God revealed his triunity in his word and his deeds -- all of which show in and of themselves his triune nature.

John Gresham Machen argued that Christianity is history (i.e., facts of history) and doctrine (i.e., their meaning).

• Christ died (fact) for our sins (meaning).

• Revelation is progressive, not corrective; it builds on what was given in the past, expanding what God has made known.

As we read the acts of God in history, the doctrine of the Trinity is revealed. Therefore, the Trinity is the basis for the Christian life and its evolution from salvation to glorification, where we will worship the triune God for all eternity. On this side of Glory, we affirm what the Athanasian Creed states, "And the catholic [i.e., universal] faith is this: That we worship one God in Trinity, and Trinity in Unity ..."

For a more in-depth (but introductory) study of the Trinity, we recommend the following resources:

• The Forgotten Trinity by James White

• The Deep thing of God: How the Trinity Changes Everything (Second Edition) by Fred Sanders

• Delighting in the Trinity by Michael Reeves

In Part 2, we discuss definitions of the Trinity and provide more resources for study.