Mission is not just another (albeit important) theme in the Bible. It is not even merely the major theme in the Bible (though I think it is also this). No, the relationship between the Bible and mission is much more fundamental than either of these assertions. As many have said, mission describes the essential character of the Bible:
the Bible does not just talk about missional things; it is itself missional.
This is the claim of Howard Marshall in his New Testament Theology: Many Witnesses, One Gospel. I quote here from A Concise New Testament Theology, which is an abridgement of the much larger work. It’s a lengthy quote but well worth reproducing in its entirety (his italics):
Mission and Theology
The focus of the New Testament writings is to be found in their presentation of Jesus as the Savior and Lord sent by God, through whom he is acting to bring salvation to the world. More specifically, they are the documents of a mission. The subject matter is not Jesus in himself (or God in himself), but Jesus in his role as Savior and Lord. New Testament theology is essentially missionary theology. The documents came into being as the result of a two-part mission: first, the mission of Jesus’ follwers, called to continue his work by proclaiming him as Lord and Savior and calling people to faith and ongoing commitment to him, as a result of which his church grows. The theology springs out of this movement and is shaped by it, and in turn the theology shapes the continuing mission of the church. The primary function of the documents is thus to testify to the gospel that is proclaimed by Jesus and his followers. Their teaching can be seen as the fuller exposition of that gospel. They are also concerned with the spiritual growth of those who are converted to the Christian faith. They show how the church should be shaped for its mission, and they deal with the problems that form obstacles to the advancement of the mission. In short, people who are called by God to be missionaries are carrying out their calling by the writing of Gospels, Letters and related material. They are concerned to make converts and then to provide for their nurture, to bring new believers to birth and to nourish them to maturity.
Recognition of this missionary character of the documents will help us to see them in true perspective and to interpret them in the light of their intention. The theology of the New Testament is not primarily ecclesiastical or ecclesiological, with a central interest in the church and its life and its structures. Nor is it an exercise in intellectual understanding for its own sake. Recognition of the missionary orientation of the New Testament will lead us to a more dynamic view of the church as the agent of mission instead of the static view that we sometimes have; it will also ward off the danger of seeing New Testament study as a purely academic exercise.
There is a quite helpful classification saying that actions in the New Testament have three aspects: doxological (glorifying God), antagonistic (opposing and overcoming evil) and soteriological (saving the lost). There is a natural tendency to give primacy to the doxological on the grounds that the highest activity of human beings is to glorify God and even what God does is intended to increase his glory. That is correct, but since the glorification of God should be the ultimate aim of all our activity, a focus on glorification may fail to express what is especially characteristic of the New Testament: the specific way in which God is glorified is through mission. The New Testament is primarily about God’s mission and the message associated with it. Similarl, the antagonistic motif is clearly of great importance, in that the powers of evil and death must be overcome if humanity is to be rescued, but this victory is not an end in itself: the triumph of the crucified must be proclaimed to humankind and become a reality for them – through mission. Again, soteriology is understood in a one-sided manner if attention is centered purely on the work of Christ as if it were an end in itself. It is significant that in Paul the fact of reconciliation achieved by the death of Christ and the proclamation of reconciliation by his messengers (leading to the human acceptance of reconciliation) belong together as the two essential and integral parts of God’s saving action (2 Cor 5:18-21).
Granted, Marshall’s focus is on the New Testament. See Chris Wright’s The Mission of God, pp.48-51, for a whole Bible perspective.