Not so long ago, those of us who use the liturgical calendar of the Western church celebrated the festival of the Holy Trinity. On this Sunday, it’s customary to confess the Athanasian Creed and maybe hear a sermon from the pastor using his one chance a year to take a shot at explaining the Trinity. This usually doesn’t work out so well, since the Trinity is not a doctrine offered up for our intellectual comprehension, but it is an important piece of the gospel itself. The trinity is an article of faith that shows us what kind of God has made it his task to create us, save us, and sanctify us.

The close connection between the Trinity and the gospel can be found in Martin Luther’s explanation of the Apostles’ Creed in his Small Catechism. Many are familiar with Luther’s Catechism, but probably wouldn’t guess that it’s one of the most important places that we find Luther teaching the doctrine of the Trinity. He teaches this doctrine very simply, for example, showing that the Father’s work of creation includes ordinary things like “house and home, wife and children, fields, cattle and all my goods” (SC II: The First Article). Luther gets down to business when it comes to what the Trinity actually means for the preaching of the gospel.

Here, Luther doesn’t launch into his discussion of the Trinity with a sophisticated account of the difference between one divine essence and the three persons who coequally share that essence. For that, one might turn to some of Luther’s other writings, especially the later disputations he undertakes in the 1530s and 1540s. These are profitable to read and indicate that Luther is a very skilled theologian of the highest order. Luther’s insights there about the Trinity are also impossible to understand without turning first to his catechisms.

On its face, Luther’s Catechism is explaining the Apostles’ Creed in terms of its three basic articles. The act of creation is ascribed to the Father, and Luther shows all the gifts bestowed by a loving and gracious God who gives us life itself and then continues to sustain our life in his creation. This continued care of God for his creatures is what we might sometimes call divine providence. God creates, but he also continually provides for us. And without his ongoing provision, we would cease to exist.

The second article of the Creed shows us the work of the Son. But this is where it’s important to look a little closer at Luther’s explanations. We often have an understandable tendency to assign the gospel to Jesus and his work on the cross. The proclamation of Christ’s death and resurrection and the forgiveness of sins for you is the most direct way to preach the gospel, that is true. But what Luther is doing in his Catechism is teaching how the gospel is an action of the whole Trinity, not just one of the persons.

There has been some recent complaint – and it’s quite justifiable – that in certain modern accounts of the doctrine of the Trinity, the persons take on the features of human psychology and social life. They come to have their own wills, personality, and tasks assigned to them. But in what way are they united? What holds Father, Son, and Spirit together in the things they mutually do on behalf of creatures?

An ancient rule inherited from the framers of the doctrine of the Trinity in the early centuries of the church can be helpful at this point. The church fathers, when explaining the Trinity, carefully point out that the external works of the Trinity are never divided. We might assign, according to Scripture, some activities to one of the persons – like creation to the Father or redemption to the Son. But because there is one God, one divine essence, and one will, each of the three persons is active in all of the activities undertaken by the God who creates the world, redeems sinners, and gathers his church.

In all that God does, the blessings of his generosity are given.

The original development of this rule was a bit technical. Because the doctrine of the Trinity rests upon a single, simple divine essence – which means there are no parts in God – the persons of Father, Son, and Spirit are not components that, when taken together, compose a single divine essence. Instead, the persons share in the single divine essence and will, so when they act, they do so indivisibly. These kinds of subtle distinctions can come off as a bit arcane, but to say that Father, Son, and Spirit work inseparably is to say that we have one God and not three, as Scripture clearly teaches. The Augsburg Confession confirms that “God is one divine essence who is eternal, without a body, without parts, of infinite power, wisdom, and goodness” (AC I 2).

Yet at the same time, such distinctions can fall into disrepair when ignored, or exploited by self-indulgent theologians seeking to speculate their way into knowledge of God’s majesty. But what Luther has done in his explanation of the Apostles’ Creed is assign trinitarian teaching to the gospel and its benefits for us. Luther follows this ancient rule by ascribing the various activities to the persons, as the Creed itself does on the basis of Scripture. But what holds these together, as far as a Christian confession is concerned? For Luther, it is the gospel.

There is one divine will, which according to Luther’s teaching is God’s mercy for us. In all that God does, the blessings of his generosity are given. Therefore, the gospel teaches us to see God not as an angry Father, but one who provides for our every earthly need in this life. The Father looks after our eternal situation as well, and so provides his Son as the sacrifice of atonement (1 John 2:2) that takes away our sins. Jesus willingly takes upon himself the sins of the world, in the process disarming the power of sin, death, and the devil. The Holy Spirit likewise “calls, gathers, enlightens, and sanctifies” through the means of grace: baptism, the Lord’s Supper, and the proclamation of the forgiveness of sins (SC II: The Third Article).

Here Luther teaches us how to put the doctrine of the Trinity to work. It isn’t a speculative doctrine meant to excite our curiosity, but instead is a dimension of the gospel. Without the gospel at the center, we are left to our own intellectual devices, which makes our sin problem worse, not better. But the gospel promises that Father, Son, and Spirit are at work inseparably to care for, forgive, and gather together the sinful creatures for whom they have one will to bless eternally.