Paul assures the elders in Ephesus that soon they will have to deal with wolves. “I know that after my departure, fierce wolves will come in among you, not sparing the flock; and from among your own selves will arise men speaking twisted things, to draw away the disciples after them” (Acts 20:29-30). The question was not if, but when. And building a wall around the church would be no help; the trouble would come from among them. Paul pulls no punches, and one can imagine the look on the Ephesians’ faces as he told them about this pending internal conflict, not unlike the reaction the disciples had in the upper room when Jesus said one of them would betray him. Every church needs an immune system for dealing with the sort of people who have a desire to make disciples in their own name, not Jesus’, and are willing to attack the vulnerable in the flock to do it. “Be alert”, Paul says (20:31). But what does this look like? Some leaders anticipate this by cultivating a climate of suspicion. “Which one of you will betray me?” Much preaching today is consistently delivered this way, causing genuine and peaceable Christians to experience undue doubt about their motives and even their salvation. Being alert doesn’t mean being suspicious or thinking evil of another. Any body that would withstanding sickness needs first to be healthy. The best way to spot a counterfeit is to know the genuine article. “And now I commend you to God and to the word of his grace, which is able to build you up and to give you the inheritance among all those who are sanctified” (20:32). Every church will deal with division, coming from within, at some point, and being alert to this fact, the best preparation is an exuberant love for and knowledge of God and his gracious gospel. This is how you get ready for a wolf fight.