Jesus was sending His followers to discipleship training.
They went out in His name to preach, and testify, and to heal and deliver. They did it and they did it successfully and they returned rejoicing!
In Jesus' Name and under His authority they had healed people and they had cast out evil spirits and had demonstrated the power of God.
Jesus rejoiced with them because He had seen the Evil One defeated by His followers obediently exercising His authority! But then He put some perspective on their accomplishments with this admonition, "However, do not rejoice that the spirits submit to you, but rejoice that your names are written in heaven."
There are several important truths to be taken from this curious statement.
1) To exercise the power of my authority be sure you are in personal relationship with me.
2) It is exciting to to have my power, but it is more important to have my provision.
3) Having God's power without living in His presence will lead to pride and corruption.
4) The power to perform signs and wonders can last for a lifetime but our place in Heaven is eternal.
5) Your position in heaven impacts your power on earth.
6) Rejoicing in what God does is good but rejoicing in Who He is much better.
Employ the power of God!
But more importantly, embrace the Person of God and live in His presence!