How did those people find out they were under false doctrine?

Les explains that these people discovered they were under false doctrine by doing what he tells people to do: they went to the Book and asked, 'What does the book say?' Les had three phone calls in a row from people in a particular denomination he feels is way out in left field. They all said their eyes had been opened and they never realized they were under such false teaching. Les clarifies that he did not open their eyes. They searched the Scriptures themselves. Truth can be elusive, but if we get into the Scriptures, the truth comes out. That is where they found out they were under a lot of false doctrine—they could not find it in the Book.