We’re on a faith journey, and each day, we make the decision to keep saying, “Here am I, Lord,” to God’s calling. That calling is to do something. When we worship, when we sing and pray, these actions are not in a vacuum. They do not serve their own purpose. We worship, sing, pray, learn, grow, and serve because we are participants in God’s movement, both God’s inner movement and God’s movement within history. Just like the prophet, when we say, “Here am I,” God actually expects us to do something. That’s not the end of the conversation.
Trinity Sunday is a strange stop on the liturgical calendar because it’s theological. Every other holy day celebrates an event in Jesus’ life or the life of the church. Trinity Sunday invites us to think about an idea. It’s a complicated idea that is fraught with bad explanations and heretical controversies. The Holy Trinity is the idea that, “We worship one God in Trinity, and Trinity in Unity… there is one person of the Father, another of the Son, and another of the Holy Spirit… they are not three Gods, but one God” (Athanasian Creed).
Within God’s inner movement, there is a sense of sending and calling. This is how God relates to God-self, and we see it throughout scripture in the ways God relates to humanity. God calls Abraham and Moses. In our reading from Isaiah, we see how God prepares the prophet for a specific task. In each calling, the one who is called has the freedom to respond, or not. “Whom shall I send?” is a question, not an edict. Isaiah demonstrates his freedom when he says, “Here am I, send me.”
This happens throughout scripture. In the gospels, Jesus calls (invites) the disciples to follow him (John 1). Elsewhere in the New Testament, we read about the Holy Spirit teaching and inspiring people (1 Corinthians 2.10). This same calling applies to us, and we have the choice of whether or not to respond. The one to whom we respond is God the Father, Son, and Holy Spirit. We respond, not to the person of the trinity to whom we relate most closely, but to all three—not three gods, but one God.
When we talk about the Holy Trinity, it gets complicated quick. To better understand it, theologians, like Karl Rahner, have developed language to describe this aspect of God. Some people might find this concept boring or irrelevant to daily life. However, putting in some of the work helps us develop a richer faith for all of the challenges we face each. Rahner describes the Economic and Immanent Trinity. The divine persons, with respect to one another, are the Immanent Trinity. That’s God’s inner working. God, as revealed and acting in salvation history, is the Economic Trinity. Rahner brings these ideas of God together, when he writes, “The ‘economic’ Trinity is the ‘immanent’ Trinity and the ‘immanent’ Trinity is the ‘economic’ Trinity.” In other words, God, as revealed and acting in history, is God’s inner working, and vice versa.
Another way to think about the trinity is through relationships. Jürgen Moltmann writes about a relational trinity. He brings it back to God’s movement in the world. It’s all about our relationship with God and one another. For Moltmann, and, as we see in Isaiah, we have agency. We have freedom and can make choices. We get to be part of this trinitarian movement. Moltmann writes, “The trinitarian doctrine of the kingdom is the theological doctrine of freedom… God unceasingly desires the freedom of his creation. God is the inexhaustible freedom of those he has created.” Moltmann suggests that we start with the three-ness of God in scripture and move back to the one-ness of God in the trinity of the three unique persons. The Holy Trinity is part of an ongoing story, and that’s where we come in.
We don’t read Isaiah as a one-time event. We don’t live our lives as if they are in isolation everything before or after. We are part of an ongoing story. Think about anything you face right now. What came before is part of that concern and what comes next is in God’s hands. No matter what it is, you can look back at how you got to this point, learn from it, accept this moment, turn it over to God, and look to the future with hope. That’s where the glory of the resurrection enters every element of life. This is where I can see Moltmann’s influence in how I’ve been interpreting the trinity. He holds everything up against the crucified God of the cross. He writes:
That is why faith, wherever it develops into hope, causes not rest but unrest, not patience but impatience. It does not calm the unquiet heart, but is itself this unquiet heart in [humanity]. Those who hope in Christ can no longer put up with reality as it is, but begin to suffer under it, to contradict it.Jürgen Moltmann, Theology of Hope
Isaiah’s encounter with God in the divine throne room of Isaiah 6 caused this kind of unrest. When the prophet responds, “Here am I, send me,” that’s not the end. If we neglect what comes next, we miss the point. Isaiah had a difficult path ahead of him. Isaiah 6.9-10 gives the prophet the next instruction, “Go and say to this people, ‘Keep listening, but do not comprehend; keep looking, but do not understand.’ Make the mind of this people dull…”
Those would be hard words to deliver, and the prophet knows that he’s about to share some bad news. In Isaiah, this is neither the first nor the last word, but we get so excited about “Here am I, send me,” that we miss the real work involved in being sent by God. We miss the other side of saying ‘yes’ to God. The hope we find doesn’t give us rest. We have a calling and work to do. It’s not about sitting under a tree, just Jesus and me. Understanding a bit of the trinity means that we reject personalism and accept being part of a divine family.
Following Isaiah’s footsteps means accepting holy assignments. God’s word is not static. It isn’t the same in all times and in all places. God speaks to different contexts. “Thus, there is a time and an occasion not only for judgment, but also for salvation. We could miss the yes because we have not heard the no.”
Try a thought experiment. Just relax and remember only you and God hear your thoughts. If you try to imagine the most difficult thing God could ask you to do, what would that be? Be honest with yourself, or try to be. Try to frame this difficult calling with as much detail as you can imagine.
What are you hoping God doesn’t ask you to do? What if God asked that question and said, “Whom shall I send?” My prayer today is that you would be able to enter the divine throne room and say, “Here am I, send me.”
 Karl Rahner, The Trinity, New York: Crossroad, 1967, p. 22
 Cf. Paul Fiddes, Participating in God, a Pastoral Docrine of the Trinity (Louisville, KY: Westminster John Knox, 2000). Without the time constraints of a sermon, I would like to connect Fiddes’ pastoral trinitarian theology with Moltmann’s relational trinity.
 Jürgen Moltmann, The Trinity and the Kingdom: The Doctrine of God, trans. Margaret Kohl (Minneapolis: Fortress, 1981), 218.
 Jürgen Moltmann, Theology of Hope, on the Ground and the Implications of a Christian Eschatology, trans. James W. Leitch (New York: Harper & Row, 1967).
 Gene M. Tucker, “Isaiah 1-39,” in New Interpreter’s Bible, ed. Leander Keck (Nashville: Abingdon, 2001), 105.