The lectionary this week skips verses 12-15 which include more of what Jesus told them to say to the towns that rejected them. Woes will come that will remind them of past destructions. Note that although the missionaries are to tell about the judgment and punishment, it's not their function to enact it.
The mission of these seventy turns out well. They report with joy, "Even the demons submit to us!"
"Satan is dead," he tells them. "I saw him fall like a flash of lightning." Why do we still fear Satan if Jesus has already seen him die? Why are we afraid of anything?
Jesus tells them that they can expect continued accomplishments--and why. They have been given authority--and that authority has been given by him. He then adds that they shouldn't rejoice as much over their power but rather over the source of any power that they are able to see or use.