Priests and Levites

This is something that came to my thoughts over the past couple of days. God appointed the priests & Levites. They were God's MPV's. Israelites were to follow the laws given to the leaders. As time progressed, these leaders began attaching their own little rituals to these laws.  So, my question is this: How did the Israelites know that they were following false teachers had Jesus not come along & told them? I mean God appointed these leaders right? They didn't have the Holy Spirit in them so the priests were all they had. So, if they did follow the priests' laws & rules being as that was all they had, were they considered righteous & still gain eternity with God? They also didn't have the word. The only exposure they had to the word was the priests' words - or that's what I would think. I know nothing about the history of the Bible so I could totally be wrong on that point. It was just a thought.