There is an interesting article about them in CT by Colin Hansen which sparked my thinking on this again.
The GC has a substantial set of foundational documents which are pretty good and which, Hansen says, "bears the unmistakable fingerprints of [Tim] Keller." These footprints relate to the ministries of mercy and justice which is a core part of Keller's theology (and the subject of one of his most well known books, entitled oddly enough, Ministries of Mercy).
Keller's view stems from his view of the kingdom of God, which he sees as present now ("already but not yet"). Thus, he appeals almost exclusively to the OT and the Gospels to substantiate this view of social ministry to those outside the church. (He once preached a message on this topic based almost completely on the book of Proverbs.) This emphasis on the OT and the Gospels is necessary since there is virtually no support for his view of social ministry in the apostles' instructions to the churches. This view of the kingdom has some serious exegetical and theological issues that have been well-addressed by others, so I won't address that here.
One of the other main theological foundations for this social justice ministry is the incarnation of Christ. They argue frequently that since Jesus took human flesh to come to earth, therefore we should "incarnate the gospel" in our dealings with the poor and oppressed. Then they look at the passages that describe life in the kingdom from the OT and the Gospels and apply them to the church, in the mistaken view that the church is the kingdom, or that the kingdom is present now.
There are significant problems with these arguments, all of which I will not get into here. I will simply touch on it briefly.
First, Jesus' incarnation was not cross-cultural ministry. Jesus was not moving from one culture to another. There is no way that we can follow the pattern of Jesus incarnation. We are already flesh, and us ministering to the poor of sick is in no way analogous to Jesus leaving heaven to die for sin. While we might legitimately debate how the church or individual Christians should deal with social justice issues, we cannot base that debate on the incarnation of Jesus. The Bible does not teach that Jesus came primarily, or even equally, to do social justice as compared to dying for sin. When the epistle says "Be like Christ" or "be conformed to the image of his Son," it is not talking about social justice. It is talking about personal holiness. Along the road of personal holiness, it is doubtless that our relationships with others will be affected. But it is a dangerous road to say that Jesus' incarnation was a model for our ministry among the poor, sick, or "socially oppressed."
Second, Jesus' life on earth was largely in a kingdom context, not a church context. The Gospels were written to the church, but we need to think very critically about how they relate to life in the church, particularly with respect to the works of Jesus (which included miracles, something absent from the incarnational ministry proponents). The OT Kingdom prophesied is a time of great change on earth, including changes in the physical/material world, government, health, etc. Those things happened during the life of Jesus to some degree because "the kingdom was hand." Yet the rejection of the Messiah by the Jewish people meant that the kingdom was "taken away" and would be "given to a people producing the fruit of it." There is no necessary rationale to see the "people producing the fruit of it" as the church. It is better to see it as end time Israel, in accord with the prophets, Paul, and John who all clearly prophesied of a revival of end-time Israel who will accept the Messiah.
These social justice issues seen during Jesus' time are not being seen now because the King prophesied to bring about these changes is at the right hand of his Father's throne, rather than on his own throne. This does not mean that the Gospels have no relevance for the church. It simply means that we must think critically about the discontinuity (as it is commonly called).
Third, this approach can undermine the authority of the Epistles which were written to direct life in the church. The absence of these social justice issues in the Epistles and Acts gives us a strong indication of the view that the church should take. Our mandate is to make disciples, not to solve poverty, or AIDS, or these other issues. The Bible does teach love for others, both in and outside the church. Yet it does not teach that the mandate of the church is social justice in society at large.
In the end, the danger of this statement by the GC is that those who do not share Keller's view of social justice ministry may be virtually excised from evangelicalism. The GC foundational documents talk about the "older evangelicalism" in this way:
On the other hand, the older evangelicalism (though not all of it) tended to read across the Bible. As a result it was more individualistic, centering almost completely on personal conversion and safe passage to heaven. Also, its preaching, though expository, was sometimes moralistic and did not emphasize how all biblical themes climax in Christ and his work. In this imbalance there is little or no emphasis on the importance of the work of justice and mercy for the poor and the oppressed, and on cultural production that glorifies God in the arts, business, etc.The "other hand" is those who denied the personal nature of sin and instead focused on the corporate nature of sin. Again, from the GC about this group (essentially the social gospel movement):
The cross is seen mainly as an example of sacrificial service and a defeat of worldly powers rather than substitution and propitiation for our sins. Ironically, this approach can be very legalistic. Instead of calling people to individual conversion through a message of grace, people are called to join the Christian community and kingdom program of what God is doing to liberate the world. The emphasis is on Christianity as a way of life to the loss of a blood-bought status in Christ received through personal faith.Contrasting these positions is not a fair comparison. These are not two extremes where both must be avoided. The focus of the gospel is not on corporate sin in any sense. Jesus did not die to save society from itself. He died to save sinners from sin. The social gospel (represented in the previous quote) was not in any way biblical. The "older evangelicals" may have had their issues in some areas, but their emphasis on the individual nature of sin, personal conversion, and "safe passage to heaven" is clear in the NT.
While we can appreciate the emphasis of the GC and clarifying and maintaining the gospel, we need to think critically about what some of their foundational documents are actually saying.