There were many false ideas floating about in Jesus’ day. Many thought the earth was flat. Jesus, as far as is recorded, never said otherwise. Others thought the sun revolved around the earth. He smiled to Himself. Their medical practices were woefully insufficient. He held His peace. Their geography maps were altogether wrong. He made no waves. They taught false ideas about religion.

He began to preach! It is interesting that Jesus did not just go along with false religion to get along with His contemporaries. He confronted spiritual error because it was dangerous.
One could go to heaven while thinking the world was flat or ignorant of the western hemisphere, but could not while disbelieving He was the Christ or practicing immorality.

Jesus went up onto a mountain one day, sat down, and began to preach (Matthew 5–7). It could be called the “It-Has-Been-Said” Sermon, because in this lesson, He systematically stated false religious positions and corrected them. He was a man of love, but He did not find this inconsistent with refuting error. Actually, it was love for souls and truth that motivated such action.