9 But avoid foolish controversies and genealogies and arguments and quarrels about the law, because these are unprofitable and useless. 10 Warn a divisive person once, and then warn him a second time. After that, have nothing to do with him. 11 You may be sure that such a man is warped and sinful; he is self-condemned.
This is a passage that is easy to over-apply and under-apply at the same time. My "foolish controversy" is someone else's core doctrine and visa-versa. If you want to defend your novel doctrine from heresy-hunters, this is the passage you turn to, pleading "can't we all just get along and agree to disagree?"
Genealogies aren't much in the loop these days, since most modern believers are from the Gentile camp and aren't going to be in the market to attach themselves to Old Testament heroes' family trees, but first century Jews were in that marketplace; Paul had to call out such arguments that would try to give the Jews in a church bragging rights over the new kids on the theological block.
Paul doesn't want us feeding the trolls. You could cut and paste this as a comment-section guide and be in good form.