In discussing the mission of the church, it is important to first offer a definition of the church; something all too readily assumed as obvious. The word ecclesiology comes from the Greek ekklesia, simply meaning assembly. The term is a compound of the Greek preposition ek (out from) and the verb kaleo (to call). It is fascinating to note that the most generic definition given by Thayer’s Greek Lexicon is, “a gathering of citizens called out from their homes into some public place.” This indicates that the church is a new citizenry with a public, not merely private calling.
In the writings of the apostle Paul the term usually has reference to a group of believers in a specific city. For example, Paul’s letters are addressed to the church of God in Corinth, the churches in Galatia, the church of the Thessalonians, and so on. Moreover, the New Testament picture of the church is that of a universal body of believers with many members but one head, Jesus Christ (Eph. 4:4). So the church is a universal and organic (living and growing) body of regenerate believers (a new humanity or citizenry) who have been reconciled to God through the death and resurrection of Christ, called out to serve their King, finding regional expression in local assemblies (or embassies) of God’s kingdom people. The theo-drama of the emergence of this great army and its part in the mission of God is a glorious one.
The mission of God is rooted in the character and nature of the triune God of Scripture. In terms of the council of his sovereign will, and for his own glorious purpose, the Father sends his Son and the Father and the Son send the person of the Holy Spirit (John 14:26; Eph. 1:11–14). This God who sends his Son and Spirit also calls out and sends his royal priesthood into the world (missio ecclesiae), anointed and ordained by his Spirit as priest-kings of the second king Adam, to participate in the reconciliation of all things to God through Christ, re-cultivating all creation into God’s garden and dwelling place in terms of his Word. Scripture is shot through with this theme from beginning to end: (Gen. 1:26–28; 9:1; Matt. 28:18–20; John 20:21–23; Col. 1:15–20; 1 Pt. 2:5; Rev. 1:6–9).
Christ Jesus reigns over all, for, having been raised from the dead, ascending to sit down at the right hand of majesty and power, all authority and judgement is in his hands, and his royal court is now in session (Eph. 1:20–23; Heb. 1:3–4; Matt. 28:18; Phil. 3:21). Those born again by the Spirit of God are now sons and joint heirs with Christ, and are appointed ambassadors of his cosmic dominion. As ‘new creatures’ through whom the power of the new creation is already at work, God’s people are sent out into all the earth to declare the good news of Christ’s reign and salvation and assert his crown rights in every area of life and thought (Ps. 2; Acts 2:29–36; 1 Cor. 8:5–6; Eph. 6:19–20; Phil 2:9–11).
As preparation and promise, this cosmic mission began with the patriarchs from Abel onward (Gal. 3:7–9; Heb. 11:4–40), and was expanded in the work and calling of the Hebrew nation as witness and blessing to the nations (Gen. 12:1–3; Deut. 4:6–8). Now in fulfilment of that covenant promise, at the end of the ages and in the fullness of time, the ‘enlarged’ Israel (John 11:50–52; Rom. 2:29; Gal. 6:15–16), the church of Jesus Christ, the household of God and people of the King, both Jew and Gentile, fulfil their glorious mandate in terms of the Great Commission. Clearly then, the mission of the church extends well beyond the reform of its institutional liturgy!
This is a distinctly and robustly scriptural perspective on the calling of God’s people, and a world-changing one. In it the church militant on earth is salt and light, pillar and support of the truth, and the very embassy of God, manifesting the manifold wisdom of Christ to all power and authority (Eph. 3:10; 1 Tim. 3:15). This vision of the church’s mission in the Western European context took decisive shape during the Calvinistic movements of the Second Reformation in Holland and the Puritan era in England, Scotland and the American colonies. Calvin was in many respects the theologian of the Holy Spirit, not just in terms of explaining the Spirit’s work of personal regeneration, but “the Spirit’s activity of renewing the ‘face of the earth.’” This emphasis distinguished Calvinistic reformed thought from Lutheranism in terms of the theology of mission. Richard Marius writes:
Luther never tried to make much of the present world, and a worldly age cannot make much of him. The Calvinists expected the world to endure, and they believed themselves to be instruments of God to convert it.... Calvinism has implanted...a perpetual dissatisfaction with our successes and a restlessness with the way things are.
This view grew inexorably out of an understanding of the regnum Christi (kingdom-reign of Christ), exalted to total pre-eminence and therefore active in the world by his Spirit and through his people. Truly biblical thought cannot tolerate the notion that the Christian faith could be limited to a vertical relationship between a person’s soul and God by individual regeneration, especially when used as a way of escaping from the responsibility of applying God’s word to all things in the common life of mankind; such a view is effectively a denial of the incarnation.
In a truly scriptural theology of mission, the church as God’s kingdom people must not only be concerned with personal salvation, or institutional church affairs, but with the reign of Christ over all things. God’s people re-present the exalted Christ to the entire creation order. As David Bosch observes, such a view “could not but give rise to the idea of mission as ‘extending the reign of Christ.’”
 David J. Bosch, Transforming Mission: Paradigm Shifts in Theology of Mission (New York: Orbis, 1998), 256.
 Richard Marius, cited in Bosch, Transforming Mission, 256.
 Bosch, Transforming Mission, 256.
In a truly scriptural theology of mission, the church as God's kingdom people must not only be concerned with personal salvation, or institutional church affairs, but with the reign of Christ over all things. God's people re-present the exalted Christ to the entire creation order.