Maybe Jesus does identify at least something about heavenly things when he speaks his most famous words in this Gospel: “For God so loved the world that he gave his only Son, that whoever believes in him should not perish but have eternal life” (3:16). When the Father adopts us, the Son unites us to himself, and the Spirit blows upon us, the outcome is eternal life. Eternal life is the life of the Triune God—the eternal life of love shared by Father, Son, and Holy Spirit. Now Jesus is talking about heavenly things, what the Trinity is. We could put it this way: The economic Trinity takes us to the immanent Trinity. Through water and the Spirit we enter the eternal life of God.

Christians need to learn only two lessons. No more, no less. Jesus himself provides this basic Christian catechesis in John 3, which recounts Nicodemus’s nighttime meeting with our Lord.

Imagine Jesus as catechism teacher and ourselves as sitting with Nicodemus in the back of the room, learning our lessons. “Rabbi,” we say to Jesus as we raise our hand, “we know that you are a teacher come from God.”

Looking sideways at Nicodemus, we turn our nose up at our fellow classmate. He is not a great student. He comes to class by night. He asks dumb questions: “How can a man be born when he is old? Can he enter a second time into his mother’s womb and be born?”  

Nicodemus’s problem is he doesn’t really trust his teacher. He says, “Rabbi, we know that you are a teacher come from God,” but doesn’t have the relational trust he needs for good discipling. He is like the many people who have come to Jerusalem for the Passover feast and “believe” (episteusan) in Jesus’s name, but whose belief is such that Jesus does not trust himself (episteuen) to them in turn (2:23–24).

Jesus is exasperated. As a trained Pharisee, Nicodemus should be a better student. But he doesn’t know the basics. “You do not know (ginōskeis) this?” exclaims Jesus. I have told you, but “you do not believe (pisteuete),” he reprimands.

Still, we should not shake our heads too quickly at our fellow student. We are only at the beginning of the lesson, in chapter 3. Nicodemus has a receptive attitude. Later in the Gospel, he tells his peers of the Sanhedrin not simply to condemn Jesus but instead to hear (askousē) and learn (gnō) what Jesus does (7:51). And by the time we get to chapter 19, Nicodemus has become a model student. He turns up at Jesus’s tomb with 75 pounds of myrrh and aloes. Now he knows and believes. He is born anew, of water and the Spirit (3:3, 5). The wind blows where it wills (3:8), even through the back of the classroom, where we thought Nicodemus belongs.

Nicodemus has learned two lessons—the only two things that make up the content of Christian catechesis: earthly things and heavenly things. Nicodemus, when he comes to Jesus in the spiritual darkness of the night, doesn’t yet know about either one of them. Jesus asks him, “If I have told you earthly things and you do not believe, how can you believe if I tell you heavenly things?” (3:12).

Much ink has been spilt about what Jesus means by “earthly things” and “heavenly things.” My hunch is that the topic of both lessons is the same: the doctrine of the Trinity. The first lesson concerns what the Trinity does (earthly things); the second what the Trinity is (heavenly things). In traditional theological terms, the first is about the economic Trinity (the economy of God’s acting among us in time and place), the second about the immanent Trinity (the inner life of the three divine persons). When liturgical calendars feature this passage from John’s Gospel on Trinity Sunday, their choice is inspired.

Theologians may have internal red lights flashing at this point, based on the dual assumption that (1) the Bible does not talk about the Trinity; and (2) the immanent Trinity is the economic Trinity and vice versa (known as Rahner’s Rule). Surely, Jesus doesn’t teach about the Trinity, let alone about the (perhaps erroneous) distinction between economic and immanent Trinity?

I suggest we loosen up on these working assumptions. Jesus begins his lesson by talking about earthly things, what the Trinity does—the economic Trinity. The lesson’s key point is that the Spirit makes us born again from above (3:3). Water and the Spirit—baptism and faith—give us a second birth. Being born a second time means that we become children all over again, “born, not of blood nor of the will of the flesh nor of the will of man, but of God” (1:12).

The Father adopts us as true sons and daughters of God. When we receive the Spirit of adoption, we cry, “Abba! Father!” with Saint Paul (Rom. 8:15). The Spirit unites us to the Son, and with the Son we are children of the Father. This, I think, is the first lesson. Father, Son, and Holy Spirit—all three persons work together in the economy of salvation to make us children of God.

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