Read: Luke 10:17-20
Nevertheless, do not rejoice in this, that the spirits are subject to you, but rejoice that your names are written in heaven. (Luke 10:20 ESV)
They returned triumphant. They felt victorious. Inspite of some of the rejection and hard heartedness of men, the disciples had done a great work. People had been healed, demons had been cast out, and the gospel message had went forth in preparation for Jesus.
I imagine that this group, mostly comprised of men marginalized by the religious establishment, felt pretty good about themselves. Jesus' words to them don't ring out as a form of correction but as cuationary concern. Of course he wanted them to heal and cast out demons. He was the one that empowered them to do it. The real matter to be rejoiced over was salvation.
In ministry it is really easy to get caught up in the wins. When things are going extremely well you start to ride a wave of success that feels awesome. Knowing God has empowered you to succeed and seeing it happen creates an opportunity to led pride sneak in. Whether you're in vocational ministry or not it is easy to let this kind of thing happen during successful seasons of life.
We must celebrate success, often. We must share stories of life change and the miraculous as they happen. But let us never forget that for each one of us the biggest cause for rejoicing in our life is the salvation of our souls.