At the college I am going to, the question was recently raised "in missions, is social development more important than evangelism?" That the question is worth asking is disturbing to me, but, given that it is being asked, it ought to be answered carefully and well. Social development is an important facet of missions, we ought not discard concerns that we may be under-emphasizing it without looking closely at what the place of social development in missions is.
First, I have previously argued that God, being the only necessary being and therefore creating all else, is therefore the most valuable that we might seek, and that we ought to seek him for that reason. In him we find total satisfaction, since he is our source. We have been created to worship God, thus we will be dissatisfied in anything but God, and this dissatisfaction is a grace to us that we might seek God and find him and therefore be satisfied in him.
Second, social development I take to mean the development of a society such that it might be more conducive to physical and moral human life. Digging wells in Africa, dealing with human trafficking, rebuilding (or building) community in the wake of longstanding war. All these are good things, we are called to do justice and love mercy.
However, since we are fully satisfied in Christ, all of those things we are dealing with in social development are secondary. They may be means to the end of evangelism, gaining trust from people, but they are not ends in and of themselves. That a person is suffering is something we should be concerned with, but the grace of God is sufficient for a person's sustenance even in that. Paul even rejoiced in his suffering.
At the same time, in regards to those sufferings that are caused by the sins of humans, the grace of God, entering those people's lives, is able to transform their lives such that they would turn from their wickedness to God. So evangelism is the most powerful implement in social development. This is not to say that we should treat the gospel as a means of social development, but that the gospel will change cultures just as it changes individual lives. If we seek first the glory of God, then all these things will be added. If we seek the glory of God secondarily, or not at all, then all our efforts in social development will be hampered by the sins of those we are trying to help.
Beyond all this, evangelism is more important than social development because the ultimate social development will occur when Christ returns in glory and totally renews the world and those who are in him will enter into his kingdom which will be developed and need no social development. If we do not seek to save the lost, that they might enter into that kingdom, then we are not seeking social development in the long term, but only in their present lives. In salvation, the saved is brought in the communion of saints, and will no longer have justification to fear humans, but only to fear the almighty God who has saved them from death to life. So that we can do the work of the ministry, do missions, because we know that God is working in us and through us, and has already accomplished his glorious purposes. Evangelism is eternal social development, any social development we do here will be but a shadow of the society we have in heaven. An image in which we may see God's glory, and therefore social development is a form of worship to God, but only a shadow, just as the songs we now sing are but a shadow of what we shall sing in heaven.
To do social development for any lesser purpose than God's glory is to do sin in doing a good act. If we desire to glorify God, then we will, in our worship, endeavor to create a picture of the kingdom of heaven on earth, and therefore, as worship to our God and king, enact social development.