Every good teacher will tell you what I am about to tell you: Test everything I say. That isn't just me trying to appear more credible, this is something the Bible actually commands and commends. In 1 Thessalonians 5:21, Paul says test all things, hold on to that which is good. In Acts 17:10-11, the Berean Jews were called "fair minded" not only for their reception of truth, but their will to test it. To test all things, therefore, is both rational and Biblical.
But why is this? Why can't you just read what I say and soak it up entirely? Put simply, it's because I'm human. I'm not God, or even one of His angels. I don't even have a rank comparable to an Apostle, yet even they were not infallible. I'm human, I haven't been commissioned by the Holy Spirit to write Scripture, therefore I will make mistakes. So will your favorite teachers.
To give a recent example, I would like to explain a minor error I held for quite some time. I have long been an advocate of liberty in food. Though I was a vegetarian when I originally wrote this article, I vehemently defended the Biblical case for a man's right to eat meat, even if Levitical law considered that kind of meat "unclean". However, I had always maintained that blood is an exception to this rule. Acts 15:20, 29 had me thoroughly convinced that the consumption of blood was still forbidden, which seemed to me to be a common theme in the dietary laws in each covenant.
This was a position I held until my friend questioned me on it. He believed I was in error, and so I listened to him and searched the Scriptures to see if he was right. And it turns out, he was. The restrictions mentioned in Acts 15 were not general restrictions intended for the whole Church for all time, but rather, they were written to a very specific group for a very simple reason: They had been saved out of a particular idolatry. These people had weak consciences which would have been defiled by further consumption of the blood.
1 Corinthians 8 further backs up this interpretation. Acts 15 also forbade this group to eat food sacrificed to idols, whereas 1 Corinthians 8 claims that the reason some are forbidden from doing this is because they still can't get it out of their minds that the idols aren't conscious. They still think of the food as having been sacrificed to a god, and so in eating it, they're effectively still committing idolatry. Nevertheless, Paul still says "But food does not commend us to God; for neither if we eat are we the better, nor if we do not eat are we the worse. But beware lest somehow this liberty of yours become a stumbling block to those who are weak."
So you can see that at one point I made an error. Not everything I believe is correct, and thus my preaching will occasionally, maybe even often, contain errors. It is vital, therefore, that you never take anything I say at face value. Search the Scriptures, agree with me where I agree with them, and disagree with me when I make such errors, lest you, yourself, make those same errors. Do the same with all your teachers.