Perhaps their intolerance for falsehood had bred a kind of inquisitorial spirit that left no room for compassion. Paul was familiar with that sort of pitfall. In the 13th chapter of First Corinthians he observed that it's possible for faithful people to do all sorts of good and noble deeds, but if those deeds are not accompanied by the critical and transforming ingredient of love, they are not worth a thing. Perhaps it was also a loss of warmth in the practice of their faith. Whatever, it's not because we want to.
Discipleship can dry into the same unappealing crust.
Like a breakfast plate left all day in the sink, it still bears evidence of that which once was appetizingly served, but now become a hard, stiff and impervious goo. Perhaps it was something of both. As it can be with us. Turn around and recover what you had at the first. Otherwise your lamp will simply go out and you will cease to be a church at all.