Christians use words like Trinity, penal substitution, and age of accountability to describe truths revealed in the Bible. Yet none of the words or phrases used above appear in the Bible in just that form.
So why do we use these words?
For many reasons, I suppose. But here I aim to give three reasons to explain why we can and should use non-biblical words to explain biblical doctrines.
Because the Bible Does not Always Name Its Categories
When we read the Bible from Genesis to Revelation, we see a progressive revelation of God through the Bible. Yet no Bible verse says “this is an example of progressive revelation.” Scripture simply progresses revelation. It does it.
But what is “it”? What does the Bible narrate progressively? The answer is that Scripture progressively reveals more and more about God and his works across its sixty-six books. The Bible does so in many ways. One way the Bible does so is through covenants God makes with people. So one might also speak of a covenant theology in the Bible.
Granted, the Bible often names its categories. So we rightly speak of the Kingdom of God because the Bible names its own category to describe this reality. But that does not always happen.
When it comes to the Trinity, the Bible progressively reveals the Father who sent his Son, and the Spirit who proceeds from both the Father and the Son. We know Father, Son, and Spirit as the one God of Israel yet distinguishable by the names of Father, Son, and Spirit.
The Father is the Father of the Son, not the Son himself; the Son is the Son of the Father, not the Father himself; the Spirit is the Spirit of the Father and Son, not the Father and Son themselves. The names Father, Son, and Spirit tell us this, while maintaining that the one God of Israel is Father, Son, and Spirit.
What a mouthful! It can be useful to have a simple word to explain what the whole Bible teaches about God. Well, the word Trinity means something like tripleness, and so the term Trinity can refer to the Father, Son, and Spirit—the one God of Israel.
Because Teachers Need to Give the Sense of the Bible to Hearers
Teachers of the Bible need to read the Bible and then give “the sense” of that reading, “so that the people [understand] the reading” (Neh 8:8). Indeed, by giving “the sense” of the Bible we need to explain it “clearly,” which in Nehemiah 8:8 translates the Hebrew word paresh. Paresh means to interpret.
And one cannot re-read the same Bible verses to interpret them without using any other words. Or else, why did the apostles through the Book of Acts interpret the Old Testament passages they were citing? Why did Hebrews do the same for the many passages it cites? The answer is that, as common sense tells us, we need to use words that people understand to explain words that people don’t understand.
A pastor on Sunday preaches the Bible’s meaning by using normal English words (or whatever language he preaches in) to explain the underlying Hebrew, Aramaic, and or biblical text that he preaches. And so interpretation and translation occur every time the Bible is preached.
As Thomas Aquinas said, “If we could speak of God only in the very terms themselves of Scripture, it would follow that no one could speak about God in any but the original language of the Old or New Testament” (ST I.Q29.A3).
Because the Bible Does not Forbid Using Non-Biblical Words to Explain the Bible
When Augustine of Hippo explains why Christians use the word persons to describe the Father, Son, and Spirit, he says, “we are allowed to talk about three persons as the needs of the discussion and argument require; not because scripture says it, but because it does not gainsay it” (De Trinitate 7.3.8, p 229).
But of course, the word person also needs to affirm what the Bible says about God. In his argument, Augustine notes that the word person might simply be the best way we can describe “Three what?” (7.3.7, p 227). God is three persons.
In terms of why Christians felt they needed a word like person to describe what is three in God, Augustine points to an earlier conflict with modalism. Modalism is the belief that the names Father, Son, and Spirit only refer to God without distinguishing the Father from the Son and the Spirit from both.
According to Augustine then, the word person particularly promoted the Biblical teaching on God against modalism (7.3.9, p 230). Years later, Thomas will explain, “The urgency of confuting heretics made it necessary to find new words to express the ancient faith about God” (ST I.Q29.A3).
The word person thus was used to clarify exactly what the Bible teaches about Father, Son, and Spirit against heretics who aimed to twist Scripture’s meaning. A modalist could say, yes, I believe in one God! Yes, I believe in the Father, Son, and Spirit! Yet modalists do not think that the Son is a person distinguished from the Father and Spirit.
Christians realized that the Bible does not teach modalism. But they sought to find a way to explain the threeness of the one God. After all, when one became a Christian, they were baptized “in the name of the Father and of the Son and of the Holy Spirit” (Matt 28:19). So the three are not one, but three and one.
How could one explain this biblical teaching and rule out modalism? One way was to use the word person. The Father, Son, and Spirit are three persons of the one God of Israel. The three are distinguishable by their names; and they really are three, not just masks that the one God of Israel wears from time to time.
God is Father, Son, and Spirit; and the Father is not the Son; and the Son is not the Father; and the Spirit is not the Father or the Son. God is one and three.
Hence, Thomas explains, “Although the word person is not found applied to God in Scripture, either in the Old or New Testament, nevertheless what the word signifies is found to be affirmed of God in many places of Scripture” (ST I.Q29.A3).
The way I like to put it is this: theological terms need to affirm all the Bible affirms without denying anything the Bible affirms or affirming anything the Bible denies.
Conclusion
These three reasons provide a plausible explanation for why Christians use words like Trinity, even though the Bible does not mention the word itself. Yet I would fully affirm that the Bible teaches everything that the word Trinity means. In this sense, the word represents what the Bible reveals about the one God of Israel—Father, Son, and Spirit.
