If St. Irenaeus taught that Scripture belongs to the Church, that it can be read and interpreted well only within the communion of the Church, then how does that affect what we believe? How does Tradition relate to theology and dogma?

Remember that in John’s Gospel, Jesus promised the Holy Spirit would lead the disciples into “all truth” (16:13). What does that look like? To explore this question, we’ll turn to another Father of the Church, St. Basil the Great. But, before doing so, let’s think about the Nicene Creed.

In most Catholic churches across the globe every Sunday, believers recite (or even sing) the Nicene Creed, beginning with “I believe in one God.” More properly, this profession of faith is called the Nicene-Constantinopolitan Creed because it is the final product of two ecumenical councils — the Council of Nicaea in 325 and the Council of Constantinople in 381. This creed (the first two-thirds of it) is the Church’s attempt to settle the fourth-century Arian controversy — an argument, in short, about the Son’s relationship to the Father, namely, about what exactly we mean by calling Jesus “God.” Arius — a popular Alexandrian priest and good preacher — argued that Jesus was not God in the same way the Father is God, saying that the Son “is not eternal or coeternal or co-unbegotten with the Father, nor does he have being with the Father.” The Son, Arius said, is in some sense a creature; that is, there was a time when the Son was not. Now, this didn’t sit well with his bishop, Alexander, who called him on it; and soon, basically, a theological war broke out across the whole Christian world.

The new lone emperor, Constantine, didn’t like all this fighting one bit, because it threatened the unity of the empire. In response, he called an ecumenical council, gathering as many bishops as he could at Nicaea in 325, who said in substance: “No, Arius, the Son is indeed of the same substance (homoousios) with the Father. The Son is certainly begotten — the ‘only-begotten’ Son, in fact, but not ‘made,’ as you, Arius, wrongly teach.” The Son is “true God from true God,” Nicaea declared, meaning that Jesus is indeed God. That, in short, was the fight the bishops of the Church attempted to settle. Though, in the end, they settled nothing, for the fighting just spilled out into new debates. They succeeded, though, in preserving a key element of the Christian faith — the full divinity of Christ — which is why the declaration of Nicaea has stood the test of time.

But the bishops at Nicaea didn’t say anything about the divinity of the Holy Spirit. Stating what they believed in, the Nicene fathers simply said, “And in the Holy Spirit.” And that’s probably because the theology of the Holy Spirit wasn’t yet an urgent issue needing articulation. But it soon would be. It wasn’t until the Council of Constantinople in 381 that the Church articulated her belief (albeit somewhat diplomatically) in the divinity of the Holy Spirit, adding that third portion of the Creed — which begins “I believe in the Holy Spirit.”

Now, the Church didn’t invent its belief in the Holy Spirit in the fourth century as some have argued. That’s not the case at all. Christians had always believed in the Holy Spirit. It’s just that it wasn’t until controversy arose that the Church struggled to state its belief in the divinity of the Holy Spirit — and then, only after a great deal of argument.

Here enters St. Basil the Great. He, alongside St. Gregory of Nazianzus, was one of the great champions of the Church’s belief in the Holy Spirit, arguing against those he derisively called the “Pneumatomachians” or “Spirit-fighters.” These, Basil argued, didn’t believe the Holy Spirit was divine like Jesus and the Father. In the fourth century, it wasn’t all that clear to some people — even after reading Scripture — that the Holy Spirit was God. Some believers in Jesus don’t believe this even today. It just wasn’t clear to some that the Holy Spirit should be ranked equally with the Father and the Son. Which, basically, was what the debate was about: Is the Holy Spirit also God?

The way the Church argued then for the divinity of the Holy Spirit was dynamic. First, theologians pointed out that if you read Acts of the Apostles and other passages in the New Testament that speak of the Holy Spirit, the Holy Spirit often acts and speaks as a person. And the argument was that only God speaks personally as the divine. In Acts of the Apostles, for instance, the Spirit speaks (Acts 1:16; 8:29; 10:19, etc.), the Spirit sends (Acts 13:4) and appoints (20:28) and directs the apostles (Acts 16:6), and so on. But this wasn’t the most persuasive argument. The more powerful argument rested on the Church’s practice of baptism.

As long as anyone could remember, Christians had been baptized in the name of the “Father, and of the Son, and of the Holy Spirit.” No one could remember differently. It was St. Athanasius who first made the argument from the Church’s practice of baptism that since only God can sanctify and save, and that — if you’re baptized in the name of the Father, the Son, and the Holy Spirit for salvation — then the Holy Spirit must be God as well. It was absurd to think otherwise, Athanaius said (“Letters to Serapion,” No. 1.30). But this was an argument based upon Christian tradition, not just Scripture. It was based on how Christians celebrated and understood baptism that informed their reading of Scripture, which enabled them to see in Scripture the fuller revelation of the Trinity.

Using both Scripture and Tradition to make theological arguments was completely appropriate, as St. Basil the Great taught in his treatise “On the Holy Spirit.” “Concerning the teachings of the Church,” he said, “whether publicly proclaimed or reserved to members of the household of faith, we have received some from written sources, while others have been given to us secretly, through apostolic tradition. Both forces have equal force in true religion.” Aside from particular theological questions about the Holy Spirit, for our purpose, the larger point is that St. Basil here cuts down to the ground the notion of sola scriptura — the argument that one needs only the Bible to make theological claims or settle theological arguments. “No one would deny either source — no one, at any rate, who is even slightly familiar with the ordinances of the Church. If we attacked unwritten customs, claiming them to be of little importance, we would fatally mutilate the Gospel, no matter what our intentions — or rather, we would reduce the Gospel teaching to bare words” (“On the Holy Spirit,” No. 27.66). Basil is quite clear that if you cut out tradition, we wouldn’t be able to read Scripture properly; rather, we’d “mutilate the Gospel.”

For Basil, this wasn’t a small point. The Christian faith itself hung in the balance. Those arguing on behalf of “Scripture alone” in the fourth century were those who argued against the divinity of the Holy Spirit. But Basil, Gregory of Nazianzus, Athanasius and others knew that wasn’t faith, for it grated against the full experience of the Christian faith. Hence, Basil’s tirade against those who rejected Tradition. “The one aim of the whole band of these enemies of sound doctrine is to shake the faith of Christ down to its foundations, by utterly leveling the apostolic tradition to the ground,” he wrote. “They clamor for written proofs and reject the unwritten testimony of the Fathers as worthless. … We will never surrender the truth; we will not betray the defense like cowards. The Lord has delivered to us a necessary and saving dogma: the Holy Spirit is to be ranked with the Father” (“On the Holy Spirit.” No. 10.25).

Now, all of this should make clear the larger point: When reading or hearing Scripture, our reading and understanding is mediated by other people’s reading and understanding, and our interpretation is influenced explicitly and implicitly by those who interpreted and lived out the Scripture before us. Even so-called fundamentalists are influenced by a tradition, it’s just that they adhere to a conceptual fiction that they’re reading the text purely, unfiltered by earlier interpretations. This is silly, Augustine basically said, for no one can claim any insight exclusively their own “except possibly falsehood” (“On Teaching Christianity,” Paragraph 8). Reading the Bible through the community is not only good, it’s necessary; it’s as it should be. Tradition is as necessary to the Faith as Scripture — our established belief in the Holy Spirit is proof of that truth.

This is what the Catholic Church teaches, and this is what we believe. Tradition is the “living transmission” of the Faith, distinct but closely connected with Scripture (Catechism of the Catholic Church, No. 78). Both “are bound closely together, and communicate one with the other. For both of them, flowing out from the same divine well-spring, come together in some fashion to form one thing, and move towards the same goal.’ Each of them makes present and fruitful in the Church the mystery of Christ, who promised to remain with his own ‘always, to the close of the age’” (Catechism of the Catholic Church, No. 80). So, what was going on, for instance, when St. Basil the Great stood upon the ancient practice of baptism, and read Scripture so as to argue that the Holy Spirit is to be ranked with the Father? The answer is that Tradition and Scripture were working together to present the true Gospel in the fourth century. The Church’s practice of baptism was basically primordial to the Christian era, predating Scripture. And referring to that primordial sacramental practice was necessary, as Basil argued, to understanding the Scripture correctly. In short, only by the light of Tradition can we understand that Scripture teaches that the Holy Spirit is God.

Father Joshua J. Whitfield is pastor of St. Rita Catholic Community in Dallas and author of “The Crisis of Bad Preaching” (Ave Maria Press, $17.95) and other books. Read more from the series here.