I wish those who unsettle you would emasculate themselves!
-- Galatians 5:12
How can Paul justify such language? And does this kind of language teach us anything about how to respond to false teaching? Or is it completely an apostolic privilege, off limits to us mere Christians?
Let's step back and see what Paul is doing. Anyone familiar with Paul's letter to the Galatians knows it is punctuated with this kind of exclamatory language. The shepherd is perplexed and heartbroken over the Galatians' apparent departure from the gospel once established, and he is livid, indignant toward the Judaizers who are leading them astray. If this were written today, we would be very tempted to chastize Paul for his tone -- and indeed, some do reject Paul's teachings today for this reason, among others (like alleged misogyny, etc.)
Galatians 5:12 shows us that Paul is being both rational and angry. It is possible to be both. Paul has not lost his temper, as harsh as his call for the heretics to castrate themselves is. (And let's not say it just sounds harsh. It is harsh.)
Paul's harsh words here are rational because he's working from logic previously established: “If you accept circumcision, you must obey the whole law" (Gal. 5:3). Using that logic, then, he's asking, “Hey, if circumcision justifies you, why not just castrate yourself altogether?”
Paul is being rational, but not coolly rational. Having anathematized the false teachers, repeated several times that they bear the penalty, that they will be accursed, he is hot with the wrath of God owed to teachers of false gospels.
But isn't he coming across . . . mean? How can this be justified?
First of all, Paul didn't invent harsh language for false teaching. They stoned such people in the old covenant. Jesus in his mercy only verbally lacerated false teachers, calling them sons of hell, whitewashed tombs, etc.
The Bible never speaks kindly of false teachers.
It suggests to restore those who fall into falsehood gently. But it never suggests treating offenders gently. Indeed, you can see throughout Paul's letter that he is pleading with the Galatians even while rhetorically punching the Judaizers. His tone when referring to the Judaizers is angry; his tone in referring to the Galatians' susceptibility is sadness. Galatians 4:8-20 is the most vivid example: you can practically hear his tears.
Here is the bottom line, assuming Galatians is a good test case, kept in the context of all the Scriptures show us about dealing with false teachers: Protecting the sheep from wolves often involves roughly handling wolves.
“Isn’t that unloving? Isn’t that hateful?”
No, in fact, it shows real love for the sheep. It shows real love for Jesus!
Real love stirs active affections, both positive and negative. Because I love my wife, for instance, I give her physical affection. Also, because I love my wife, I will do physical violence to anyone who attacks her.
Do you see how that works?
Because God loves justice he hates sin.
Because God loves the truth, he hates lies.
Because God loves his Son, he hates teaching that demeans his Son, and legalism does that. Heresy does that.
Therefore, because God loves his children, he hates false teaching. And we ought to take the kid gloves off with false teachers, if our love for Christ and his church is real.
There is gospel to be found in this harsh language. Because God loves sinners, he does the harsh thing of sending Christ to suffer violence, to deal harshly with sin by being dealt harshly with by sin, and laying his life down for the sheep.
Christ was cut off, cursed, made sin, made heresy, that we might be brought into the truth. The cross is the ultimate harshness to sin. What a loving thing to do to conquer that sin and rescue sinners.