Should Christians Rejoice About Exorcisms and Other Big Ministry "Wins" ? #191 Reading Luke 10.

In Luke 10, Jesus sends out 72 of His followers to go and share the good news, and their mission is remarkably successful. They come back overjoyed, remarking that even demons had submitted to their names. Jesus then sits them down and challenges them on this, turning their rejoicing away from marvelling at their success, towards marvelling at God's grace. Why did He do this?