What if someone is wrong about what the Bible says? If someone is teaching others inaccurately about God or the Bible, doesn't that basically make them an employee of the devil himself? Aren't we supposed to watch out for false teachers / preachers?
Why it matters:
The Bible gives a lot of warnings about following after false teachers, and that people who follow such teachers are probably going to hell. That's a big deal.
This article assumes that the list of things on the right is true before we even begin.
This article assumes you already know:
God exists
The Bible should be taken seriously
Short answer:
If a Biblical teacher is wrong about something that the Bible says is important, then it matters a lot. Otherwise, it shouldn't matter at all...but the culture you live in might make it matter at least some, if you care about others.
2nd Peter 2:1 -- But there were false prophets also among the people, even as there shall be false teachers among you, who privily shall bring in damnable heresies, even denying the Lord that bought them, and bring upon themselves swift destruction.
Matthew 24:24 -- For there shall arise false Christs, and false prophets, and shall shew great signs and wonders; insomuch that, if it were possible, they shall deceive the very elect.
You can get a sense of how serious an issue the Bible regards this question from these passages.
It is possible to be in an eternal amount of trouble