Back in the day, when I was working with Christian students, I was once asked to give a little talk about some aspect of eschatology. I duly delivered, and only discovered afterwards that by a misfortune of timing a local church student worker had also spoken to the issue at hand during the week, and moreover had expressed opinions rather contrary to my own. The students were a little flummoxed. Being good conservative evangelicals, they were committed to the notion of truth, and they were aware that the differences they were hearing were not the sort of thing that could be explained as different perspectives or any such thing. But unfortunately they were not equipped with a category for 'Christian teachers having differing interpretations' - if we were teaching differently, one of us must be a false teacher. To avoid this conclusion, they opted to assume that they had simply misunderstood the talk in their local church. They were not inclined to consider either of us a false teacher, and so they had to assume that we had not, in fact, disagreed - despite the evidence of their ears.
This story goes a long way to explaining some of my ambivalence about the term 'false teacher'.
What is clear, to me at least, is that on this occasion at least one of us was teaching falsehood. I am, of course, inclined to think it was the other fellow. Our views on the question under discussion were irreconcilable, at least in substance (although doubtless there were elements of truth present in both positions). If what we were talking about was a real thing, then there is no doubt that one of us was substantially wrong (and of course, both of us may well have been entirely wrong; what is certain is that we were not both right). But it seems to me that when Christians use the category of 'false teacher' they must mean more than this - more than a different opinion or apprehension on one matter of eschatology. Since every Christian teacher has, at least from time to time, taught falsehood - by error of positive teaching, by omission, by neglecting or just failing to communicate clearly - the sort of broad category being deployed by these students would leave none of us standing.
So I'm keen to have a category for teaching falsehood without being a false teacher.
But there is no doubt that the NT does present us with people who have gone beyond this - people who are, deliberately or naively, leading the people of God astray through their teaching in a way which directs them away from the true God and away from right living. And I've been thinking recently that we need to have the courage to recover this category and treat those who fall into it in an appropriate way. This isn't an alternative to having a certain tolerance for error; it goes alongside it. In fact, the parameters of orthodoxy are such that there is a wide field over which we can range without stepping beyond the bounds, and certainly within that field we can be and often will be 'wrong' - but without being destructively wrong.
I think it is that destructiveness that characterises the true false teacher.
Of course all error is to some extent destructive. Truth builds up, falsehood pulls down. But there are two particular types of error which are flagged up in the NT as destructive: error that leads people to such a false understanding of the deity that the God they worship is no longer recognisable as the Holy Trinity; and error that leads people into such egregious moral behaviour that their lives no longer bear the stamp of that holiness without which no one will see God. These errors destroy people.
Because they destroy people, the appropriate response of the church, and especially of the pastors of the church, is an almost absolute 'no'. The determined false teacher must of necessity be excluded from the church, treated as a pagan. There is mercy - there is always mercy! - but in this case it needs to be mixed with fear, fear lest the destructive tendency of false teaching be let loose amongst God's people.
Looking at the confusion in the church on a hundred issues - from things as central to the understanding of God as the divinity of Christ, and things as essential to the moral life as the nature of marriage and sexuality - it seems to me that some lines need to be drawn. Because I am a product of my time, and because I have the sort of brain and temperament that always wants to nuance everything and see the shades of grey, drawing lines makes me deeply uncomfortable. But the alternative is worse, much worse: the destruction of faith and morals, with consequences which are potentially eternal.