28 “So guard yourselves and God’s people. Feed and shepherd God’s flock—his church, purchased with his own blood[h]—over which the Holy Spirit has appointed you as leaders.[i] 29 I know that false teachers, like vicious wolves, will come in among you after I leave, not sparing the flock. 30 Even some men from your own group will rise up and distort the truth in order to draw a following. 31 Watch out! Remember the three years I was with you—my constant watch and care over you night and day, and my many tears for you.”
Church growth is not always a good thing. There are people who join churches and they are not believers. It’s great when we are welcoming visitors and enquirers but don’t confuse that with growth of the church itself. When people are able to become members and participate without their relationship to God and need for salvation being challenged then that’s not good. Furthermore, there are sadly people who turn up with their own agenda. They are looking for a group that they can shape to their own agenda. Now, at its most benign, this will be that they are looking for a group to meet their needs and to keep them happy, they are looking to be comfortable. At its most sinister, they are looking for people they can manipulate, control and abuse.
Paul said that even within the churches there would be people who were there to cause harm. The false teachers were not outside the church, they were inside it. No doubt when they joined, everyone was excited. No doubt these people looked competent, genuine, committed, energetic, charismatic. They may even have drawn others in. Yet they were not sheep, they were wolves.
I am sitting in my garden now, it’s a reminder of my constant failure as a gardener. Yet despite the fact that I put nowhere near enough time into the garden, despite the fact that I a pretty clueless about it, stuff is growing. The problem is that the stuff that is growing isn’t good. It’s the weeds, thorns, thistles and nettles that are growing. Not all growth is good growth.
This is why Paul says that the responsibility of the elders is not just to feed the flock to encourage growth but to guard the flock, to protect against danger.
 Acts 20:28-31