The events of the public ministry of Jesus were history. His death, burial and resurrection were things of the past. Jesus had made some appearances since being raised from the dead, the these verses were his departing commands to his closest disciples. They contain those words which we call the "Great Commission," which extend even to us and become the basis for the church's ministry of evangelizing the world.
One special note for those who are familiar with this section of scripture is we often start quoting with the command of Jesus, "Therefore go and make disciples of all nations...." We fail to read and remember the verses that lead up to the command. Notice, the eleven went to Galilee, to the exact place where Jesus had told them to go. Then they saw him. They worshiped him, but some doubted.
Was there doubt in the ranks of the remaining eleven? The very ones who had followed him through all the ups and downs, in good times and bad, those who were witnesses to his resurrected state. How can it be, even after all that, there were some that still doubted?
Before we find an answer to that, we must make a contemporary glance at those of us who are disciples of Jesus. His authority in heaven and earth has been established and it is by his authority that we are commanded to make disciples of every nation. We preach and proclaim that every Christian is commanded to actively participate in evangelizing the world.
Even when understanding that, we must admit that we have fallen short of being obedient to the Great Commission's commands. We may hear it preached from the pulpit, and drop a few bucks in the collection plate, and feel confident we are supporting the spread of the gospel. I would never discourage your financial support to missions and evangelism, but there is a trend among us just like that of the eleven mentioned at the end of Matthew 28. Even today, some see him, they worship him, but some doubt. They may doubt the authority of Jesus, or they may doubt their own ability to be making disciples of all nations, but the doubt is there.
Look again at the closing words of Jesus' commands. "And surely I am with you always, to the very end of the age." My premise is this. When our doubts have been erased concerning Jesus being with us now and to the very end, only then will we be instruments in his hands, bringing others to him.