How do we know that false doctrine is a danger for Christians?

The danger of false doctrine is highlighted throughout the New Testament, with various warnings about false prophets and teachings. In the sermon, it is emphasized that false doctrine does not present itself overtly; rather, it sneaks in like leaven, subtly influencing beliefs and practices until it alters the entire faith of an individual or community. Christ's awareness of human nature led Him to caution His disciples, reminding them that those who are spiritually secure can still fall prey to temptation and error. The prevalence of false teachings throughout church history underscores the need for constant vigilance against the leaven of the Pharisees and Sadducees.