What makes a teaching worth believing: being Les's own idea or being shown from Scripture?
A teaching is worth believing when it is shown from Scripture, not when it is merely someone's own idea. Since Scripture is the inspired Word of God and is to be taken literally, demonstrating truths from it allows people to read and believe them.
Les explains that he always wants to show everything from Scripture. He says when he has an idea, he expresses it as just that—his own idea—and cannot prove it from Scripture. But when a teaching can be shown from Scripture, he trusts people will look at it, read it, and believe it, because Scripture is the inspired Word of God, which he takes literally. He illustrates this by saying we take historical accounts like Washington crossing the Delaware literally, and we should do the same with Scripture, not dreaming up another meaning.