Opinions shift, change, twist and turn. Facts are permanent and unbending.
God's Words are fact.
Bible teachers and pastors can't help but include thoughts and opinions when explaining Scripture, but good teachers make their listeners aware when they do this. And they never share thoughts or opinions that contradict Scripture.
For example, a pastor may tell his congregation what he believes Martha was thinking when she ran to meet Jesus after Lazarus' death and what Mary was thinking when she waited. I've heard this done to illustrate some aspect of Christian faith. But it's important to know that the Bible doesn't tell us what Martha and Mary were thinking.
Unfortunately, some teachers purposely present their opinions as Scripture or take Scripture passages out of context and twist the meaning.
That's why it's so important that we know Scripture for ourselves.
Image source: Billy Frank Alexander