A theology of missions is a subset of Christian theology that examines the motivation for and necessity of evangelism, or converting others to the Christian religion. Theology of missions is a very practical branch of theology, since the conclusions drawn from it directly effect the goals of churches and individuals. Generally speaking, the goal of any Christian mission work is to spread the Kingdom of God, but evangelical and liberal groups are likely to differ in their interpretation of what that means. Evangelicals typically view the main goal of missions to be converting people to the Christian faith, while liberals are more likely to focus on social issues in their mission work. Both groups will typically be supportive of some aims of the other, but their methodologies and focus will differ.
At the heart of most evangelical mission practices is the belief that eternal salvation and entrance into heaven come only from faith in Jesus Christ. Many evangelicals believe that those who have not accepted Jesus will be condemned, and define the Kingdom of God as the people who explicitly identify themselves as Christians. This view is known as restrictivism or exclusivism and is based on scriptures such as John 14:6. As quoted in the New International Version translation, Jesus says, "I am the way and the truth and the life. No one comes to the Father except through me." As a result of this belief, evangelical theology of missions usually places a huge emphasis on preaching and teaching among "unreached" people groups — ethnic or social groups who have never been taught about Jesus — with the explicit goal of converting them to Christianity.
Other Christian groups have a more open view of salvation, believing that at least some non-Christians will be saved. People who subscribe to this view are less likely to focus on conversion and more likely to focus on practical, here-and-now relief from poverty, sickness, or oppression. Some of these groups believe in what is known as liberation theology. According to this view, the Kingdom of God may be defined as areas where Christ-like ideals are carried out.
Practitioners of these two groups may find fault with the theology of missions of the other. Liberals may criticize evangelicals for being too "other-worldly." They may point out that a large amount of Jesus' teachings had to do with practical social matters, rather than questions of what happens after death. Evangelicals, on the other hand, may think that liberation theology stops short of addressing the actual question of salvation and Christ's uniqueness, perhaps as a result of fearing to give offense.
Despite the differences in the theology of missions in these two groups, there is often overlap in the actual practice of missions. Evangelical missionaries may seek to address the physical needs of the people they work with, just as liberation missionaries would. This is typically the first step toward building relationships that might eventually lead to conversion. Liberation missionaries often may not believe that conversion is essential for eternal salvation. They may, however, believe that conversion to the Christian faith will help to bring about social change, and so will teach about Christ when they feel it is appropriate.