“Well, you know. If the preacher says it, then it’s got to be true. I’ll just go with whatever the preacher says. He knows what he’s talking about.” How many have said (or at least thought) such words? Too many. 
The truth is that every preacher is subject to error. Every one of them! They are human, and as such, they are capable of saying something (intentionally or unintentionally) that is not in harmony with God’s Word. So, what are we supposed to do?
When Jesus was transfigured in Matthew 17, the great lawgiver (Moses) and the great prophet (Elijah) appeared with Jesus and were talking with Him. When Peter wrongly elevated Moses and Elijah to equal tabernacle level with Jesus, “a voice” from heaven pointed at Jesus and said, “Hear Him!” (17:5). Every single thing that we hear needs to be run through Jesus-i.e., through His New Testament! Don’t believe everything you hear! Only “hear” what is in harmony with what you “hear” from His Word!