"Now a Jew named Apollos, a native of Alexandria, came to Ephesus. He was an eloquent man, competent in the Scriptures. He had been instructed in the way of the Lord. And being fervent in spirit, he spoke and taught accurately the things concerning Jesus, though he knew only the baptism of John. He began to speak boldly in the synagogue, but when Priscilla and Aquila heard him, they took him and explained to him the way of God more accurately. And when he wished to cross to Achaia, the brothers encouraged him and wrote to the disciples to welcome him. When he arrived, he greatly helped those who through grace had believed, for he powerfully refuted the Jews in public, showing by the Scriptures that the Christ was Jesus."
- Acts 18:24-28
There are times when polemics are necessary. This of course is often unpopular in the church because it feels "mean" to modern sensibilities. "Let's just say what we believe," it is reasoned. "There's no need to point out another's error." It would be nice I suppose if we never needed to identify errors. It would be nice if there were no errors to refute. But one of the ways the apostles served God's people was through polemic - speaking out against specific errors. Indeed, much of the Bible itself is polemic.
In our own day, when competing truth claims often sit side-by-side, it has become essential for sermons, statements of faith, and the like to contain both affirmations and denials.