When Jesus had first appeared to them on Easter Day in the Upper Room, they had been filled with a strange terror, but all that was now a thing of the past.  During the 40 days which followed, they had looked forward to each meeting with him, but now those meetings had fulfilled their purpose.

Jesus had used them to give to his Apostles the sure conviction that he was indeed risen from the dead and alive for evermore.  And he had also set before them their worldwide mission of building the Kingdom of God on earth, that is, of extending the Sovereign rule of God over the hearts and minds of men, women and children.

Now it was almost time for them to go out into the world in his Name, and so it was necessary to tell them in an unmistakeable manner that from now on they could expect no more Resurrection appearances of the kind to which they had become accustomed.  No more would he appear in their midst as in the Upper Room, and it was for that reason that this leave-taking on the Mount of Olives had so dramatic an air of finality.