God has graciously given the church time, great time, to take the gospel to every tribe and nation. This great time also affords the church a precious opportunity to achieve a deeper understanding of her faith, for we do not really understand something until we are able to explain it in our own words to others. Christ—which is to say our understanding of Christ—grows as the church interprets and acts out the truth of the gospel in ten thousand places.
The company of faith transmits the faith not only by translating Scripture but also by transposing it: performing the gospel; living out what is in Christ; speaking and displaying creative understanding. In a word: the church improvises, in new terms for new contexts, the faith once delivered to the saints. Improvisation is ultimately another way of speaking about creative understanding.
Note well: it is important not to confuse improvising with innovating. A jazz musician improvises freely within certain melodic and rhythmic constraints. Theatrical improvisers, similarly, act spontaneously in ways disciplined by the initial premise of the scene. In each case, there is something historical, in the sense of a prior action, which anchors and orients improvisation.
Peter’s sermon in Acts 2:14–36 clearly sets out the central themes of redemptive history. Improvising is the process of discovering the full meaning potential of Scripture by continuing the disciples’ story, speaking new lines and acting out new scenes in new cultural contexts in ways that preserve the evangelical truth and action at the heart of the drama of redemption.
A Pastoral Endeavor
Developing doctrine in the church is one more in a series of improvisations: the disciples’ story is an improvisation on the history of Israel. Jesus Christ is himself an improvisation on a covenant theme: God’s steadfast love and righteousness. In each case, there is both creativity (newness) and fidelity to what preceded (sameness).
Improvisation accents the importance of both speaking and acting out faith’s understanding. The development of doctrine belongs not to speculative but to pastoral theology. In each case, doctrine helps the church to know what to say, think, and do in the face of new challenges. Is it proper to speak of the Holy Spirit as God? Should we affirm Jesus’s “descent into hell,” and if so, what should we mean by it? What kind of comfort can we offer to the bereaved parents of unbaptized children? These questions are similar to the ones faced by the church fathers at Nicaea: does Scripture depict the Son as the greatest of God’s creations or as the same as God?
In each case, doctrine helps the church to know what to say, think, and do in the face of new challenges.
Missiologist Andrew Walls rightly reminds us,
The purpose of theology is to make or clarify Christian decisions. Theology is about choices; it is the attempt to think in a Christian way. And the need for choice and decision arises from specific settings in life. In this sense, the theological agenda is culturally induced; and the cross-cultural diffusion of Christian faith invariably makes creative theological activity a necessity. 
The development of doctrine is a matter of thinking biblically in new situations. Scripture shapes our vision of the whole, instills mental habits, forms the desire of our hearts, and trains us in the way of discipleship. Doctrine is essential for training in discipleship, and that includes missiological improvisation—knowing how to go on in the same gospel way in different situations.
Essential to the Church’s Mission
Here is the end of the evangelical matter: the triune God has acted in our world and summons the church to play a part in the triune drama of redemption, spreading and embodying the good news that the Father is renewing all things in the Son through the Spirit. Doctrine helps the church understand God, the gospel, and her own nature and mission. The challenge of theology is to direct the church rightly to participate in the same drama of redemption in different conceptual contexts and cultural-linguistic forms.
It is not that doctrine is infinitely revisable, but rather that doctrine is infinitely realizable, for biblical judgments may be formulated in a variety of languages and cultural settings. Doctrinal development is ultimately a matter of the church’s faith improvisation in accordance with the Scriptures and with earlier faithful improvisations (e.g., creedal formulations).
Truth in God . . . is unchangeable; but truth in man, or the apprehension of it, grows and develops with man and with history. Change . . . is not necessarily a mark of heresy, but may be a sign of life and growth, as the want of change, on the other hand, is by no means always an indication of orthodoxy. 
The development of doctrine is part and parcel of the mission of the church. Doctrine helps disciples individually and corporately to make right decisions about what to say and do in order to participate rightly in and continue the same drama of redemption in which Israel, Jesus Christ, and the apostles played leading parts.
The purpose of theology is to make disciples, players in God’s drama of redemption who are able to play their parts with faithful and creative understanding.
 Andrew F. Walls, The Cross-Cultural Process in Christian History (Maryknoll, NY, and Edinburgh: Orbis and T. & T. Clark, 2002), 79.
 Philip Schaff, The Creeds of Christendom, 6th ed. (New York, 1931), 87.
This article is adapted from “Improvising Theology according to the Scriptures: An Evangelical Account of the Development of Doctrine” by Kevin J. Vanhoozer in Building on the Foundations of Evangelical Theology: Essays in Honor of John S. Feinberg, edited by Gregg R. Allison and Stephen J. Wellum.