continued from yesterday
The Great Commission is directed at the eleven disciples. Did Jesus in Matthew mean it to apply to more than just these eleven? After all, Jesus specifically directs his instructions to the eleven in Matthew 28. He does not direct it to the other Jews who followed him around, listening to his teaching. He does not direct it to those who will later believe in him like you and me.
I think there is good reason to think that Matthew wanted his audience to see themselves as part of the Great Commission as well. For one, I suspect that most of the disciples were already dead by the time Matthew was written. If Matthew dates to the time after Jerusalem's destruction, as most experts think, then Peter and James were certainly dead already. Yet Matthew 28:20 says that Jesus will be with the disciples to the end of the age. The implication is that Jesus was still with the audience of Matthew, even if the disciples were passing.
The way that Matthew seems to blur the time before Jesus' death and after his resurrection gives us another reason to believe that Matthew was not written simply to record what Jesus did while he was on earth. It is not simply a history book written out of antiquarian interest but was meant to speak directly to an audience some forty to fifty years later. The "mission sermon" of Matthew 10 seems to address not only the mission of the disciples while Jesus was on earth but the one they would conduct after his death. The way the Pharisees are treated probably speaks not only to Jesus' own interaction with them but to the period in the 70s when they were the primary authority left within Israel.
So if Matthew spoke so strongly to the Jewish Christians of its day, then presumably its climactic mission was also for them as well. Perhaps Matthew still has traces of the expectation that the end would come very soon (e.g., 10:23; 24:34). But it draws an arrow that points beyond the first mission to an ongoing mission that continues today, because it already points beyond the lives of the first disciples.
On the one hand, we have good reason to think that some early Christians saw the mission to all the nations largely finished in the first century. Sometimes Christians have pushed for taking the gospel to unreached people of the earth because of verses like Matthew 24:14: "this gospel of the kingdom will be preached in the whole world as a testimony to all nations, and then the end will come." The problem is that we are defining "whole world" on our terms rather than those when Matthew was written. Colossians 1:23 says that the gospel had already been preached "to every creature under heaven" way back in the first century. The "whole world" of that day was largely restricted to the lands surrounding the Mediterranean. 
Yet surely the spirit of these statements continues on, not least because the Christians of the first few centuries understood Matthew to be Christian Scripture. When the early Christians came to see Matthew as part of a new canon, a "New Testament," the church was saying through the continued inspiration of the Spirit that these words were not just words for the first century. They were not just words for the time when Jesus was on earth. They were not just historical record. But these words in some way continued to speak to Christians one hundred, two hundred, now two thousand years later.
So without even thinking about it, most of us today understand that we are included in that commission to the eleven disciples. We understand that the Spirit of Christ and the heavenly authority of Christ continue with us today. We understand that we are also in the business today of making disciples of all the nations and teaching them Christ's commandments.  We still baptize.
Our world is much bigger than theirs was. We are aware of many more nations to reach with the good news. So while Matthew and Paul may not have had New Guinea in mind, the way we have come to read these passages about the mission fits perfectly with the Spirit of their mission.
What was the good news of the kingdom again? ...
 This is an ironic by-product of viewing Matthew in modern historical terms. If we insist on viewing Matthew's primary goal as telling us only about what Jesus did and said for three years while he was on earth, then we have to justify applying it to the church that came afterwards. On the other hand, if Matthew writes a version of Jesus' life that "translates" him for Matthew's audience, then Jesus' words in Matthew transcended his earthly situation from the very start and applied directly to the church that followed.
 We are often rather unsophisticated in our ability to handle figurative language in our reading of the Bible. Human language is full of figures of speech, metaphors, hyperbole, and all sorts of idiomatic expressions. What a phrase like "every creature" means depends on how the person using the phrase means it, not on how it strikes me in my "dictionary."
 The phrase, "all nations" could also be translated as "all Gentiles." While it is hard to believe that Matthew 28 only has a Gentile mission in mind (surely the eleven were also meant to continue their mission to the Jews), the Great Commission probably did originally have a strong connotation of the mission to Gentiles after Jesus' earthly focus on the Jews.