Matthew 16:6&12 "Watch out!" Jesus warned them. "Be aware of the yeast of the Pharisees and the Sadducees." 12. Then at last they understood that he wasn't speaking about the yeast in the bread, but about deceptive teachings of the Pharisees and Sadducees.
A little deceptive teaching can effect your whole belief system, just like a little yeast changes the structure of a whole loaf of bread not just part of the bread...but the whole thing.
If we run a stop sign that we don't see, we have still run the stops sign. If we are caught by the police we can still get a ticket... we have still broken the law. We are responsible for God's law in the same way. It is all written down for us to read for ourselves. There were things that I believe that were wrong, things I have head people say about the Bible, if I had never picked up my Bible and started reading it I would have never known. Those things at the time shaped my decisions. I am still accountable for those actions. By reading my Bible and learning what I needed to know, I was able to ask for forgiveness and have those sins thrown into the sea of forgetfulness. Next time I will be able to do better, because now I know! What if I had never picked up my Bible and started reading?
If we don't know a sin is a sin because of something someone else said, it can effect our whole lives. It, like yeast in bread, can change who we are, how our lives are shaped. It is up to each one of us to know what is right and what is wrong. In these verses Jesus is warning us that it is important to know the difference. He is saying that if we don't know the difference our whole lives can be effected.
When we read our Bibles and know the words enough, we can recognize the red flags of untruth. If we know God's word enough to see a red flag we can then go to God's word and find out the truth. In today's world with such technology we don't even have to know verse and chapter. We just have to know part of the story, then with those words we can find the verses that give us the truth. It is important that we know God's word for ourselves.