Jesus died for me.
Anyone who believes this simple sentence has entered the sphere of Christian faith, and has learned the one thing that God is concerned to teach his human creatures, in order to bring them into his school for all further lessons. “Jesus died for me” is knowledge that can be grasped by anyone. It is not a truth restricted to the leading intellects of an age, or scholars with enough leisure time to include theology among their academic pursuits. It is truth which proves itself by its ability to “come to the unlearned, the young, the busy, and the afflicted, as a fact which is to arrest them, penetrate them, and to support and animate them in their passage through life.” At the same time, Christian faith does not exhaust itself at the level of simplicity, and so there are depths in this confession which invite further search and inquiry. The prepositional phrase “for me” is loaded with possible meanings, and the verb “died” is not normally the carrier of good news outside of this strange sentence. What, asks faith, is the secret of this sentence’s active subject, Jesus? That is the crucial question, because he is the one who establishes the meaning of “died” and “for me.”
By asking these questions, evangelical faith seeks theological understanding, in just the same way that “faith seeks understanding” according to Anselm of Canterbury’s famous definition. Evangelical theology starts out from the gospel story (Jesus died for me), and explores the staggering theological claims that Christians are committing themselves to when they say such things. In particular, evangelical theology takes seriously the Christian claim that the person called Jesus is a person who is God, and belongs in the Trinity as the eternal second person. He is “the Son” from the formula “the Father, the Son, and the Holy Spirit,” and he is precisely the same one who went to the cross, undergoing and overcoming death for our salvation. The Christian church has confessed this truth since the early centuries, and stated it classically at the second council of Constantinople (in the year 553) with the saying: “One of the Trinity suffered in the flesh.” You could update that for modern sensibilities as “One of the Trinity died on the cross.” Though the doctrine is biblical, has deep roots in Christian history, and commends itself as reasonable and practical, it has been denied by a variety of modern theologies. Disproving those denials would be a worthwhile (double negative) task, but the more important task is the more directly constructive one, of clarifying the doctrine itself for the benefit of those who desire to know what they are believing when they believe.
Something remarkable happens during the passage from simple belief in the gospel to complex theological understanding. When simple faith’s straightforward statements are elaborated in fully-developed theological systems, theologians are compelled to hold together a vast number of details without losing hold of their original unity. You could say that the one idea of the gospel becomes inwardly complex, and whole regions of doctrine become apparent within it. The assertion that one of the Trinity died on the cross unfolds itself as a series of interconnected claims about the doctrine of the triune God, the pre-existence of Christ, the incarnation, the death of Christ, and redemption. Which of these things should be said first, since all of them remain linked together as closely as they were in the simple expression that Jesus died for me? Pity Christian theologians: they have to say everything at once, but they cannot. This tension is probably felt by scholars in a wide variety of non-theological fields, as they try to articulate the details of their subject in light of the whole field, and the whole field in light of all its details. It is a tension present in each of the sub-topics of theology, such as the doctrine of humanity, where the central idea is a twofold statement: humanity is in God’s image and also radically fallen. But even if a theologian leaves aside all the details and only tries to say the one main thing that makes Christian faith what it is, the one main thing includes within itself the three gigantic doctrines of atonement, incarnation, and Trinity.
Though the body of Christian truth is made up of a great many doctrines, perhaps hundreds of them, there are only three great mysteries at the very heart of Christianity: the atonement, the incarnation, and the Trinity. All the lesser doctrines depend on these great central truths, derive their significance from them, and spell out their implications. Each of these three mysteries is a mystery of unity, bringing together things which seem, in themselves, to be unlikely candidates for unification. The Christian doctrine of atonement describes reconciliation between the holy God and fallen man. The Christian doctrine of the incarnation confesses that the complete divine nature and perfect human nature are united in the person of Jesus Christ. The Christian doctrine of the Trinity says that the one God exists eternally as three persons, Father, Son, and Holy Spirit.
Furthermore, atonement, incarnation, and Trinity are directly related to each other in a particular way. The good news of salvation is that Jesus Christ accomplished the reconciliation of God and man through his indissoluble life, death, and resurrection (the atonement). To have accomplished such a feat, Jesus Christ must be someone who belongs equally to the divine and human sides, so that his work is grounded in his person. The logic of the gospel compels us to say that to be the savior, Jesus must be God and man (the incarnation). Once we have seen the divinity of Jesus, it is merely a matter of intellectual consistency to acknowledge that in some way Jesus must be part of the very definition of what it is to be God. The implication, necessary but still surprising, is that the one God includes God the Son who brought salvation, God the Father who sent salvation by sending the Son, and God the Holy Spirit who brings it into human experience (the Trinity). The doctrine of the Trinity is the revision of the Old Testament understanding of God made necessary by the revelation of the God-man in the gospel. Thus to follow the order of discovery, up from our experience of salvation to its presuppositions: atonement requires incarnation requires Trinity. Or to follow the order of being, down from the most essential presuppositions to their effects: Trinity makes possible incarnation makes possible atonement.
The whole trip is necessary if one of the Trinity died on the cross.