The population of planet Earth is estimated to be about 6.5 billion people.  Of this number, some 2 billion people claim to be Christian.  As Christians, we are a minority on planet Earth.  This being the case, what do we mean when we say we must "finish the work?"  What would that look like?  How would we know when it was "finished?"  Will it be "finished" when we have churches in every country registered by the United Nations?  Strictly speaking, we cannot as an organization, however committed and well-intentioned, "finish the work."  Only the Holy Spirit can do that.  We are to be co-laborers with Him and not the other way around.