What does Mark 7:12 mean?

The relationship between the Pharisees and the people is an interesting one. The Pharisees have no legal authority. They have no direct ties to the priests or the temple. They are lay-leaders who study the Mosaic and oral laws thoroughly and try to live by what they read. In doing so, they come to value the law more than the law-Giver. They see people through the lens of the law: do they follow it or not? This is in contrast to seeing people through a lens of God's love and grace. The Pharisees' discipline deserves a measure of respect (Matthew 5:20), but their self-assumed prophetic power over the people is unhealthy and unbiblical.

Even so, it is very effective. Gamaliel was a Pharisee on the council, a teacher of the law, not a priest, when he suggested that the Christian movement would die out if it was not of God (Acts 5:33–42). We're not sure if Paul was an "official" Pharisee, or if he was just studying to be one (Philippians 3:5), but he had the authority to capture, imprison, and vote for the deaths of Christians, even those outside of Israel (Acts 26:10–11).

When Jesus says that the scribes and Pharisees do not "permit" the Jews to break a vow for the sake of his parents, He expresses the influence the teachers hold over the people. That hold is despite some serious contradictions. 1. The Mishnah has sections that prioritize the commandment over the rash vow, but apparently some of the scribes and Pharisees didn't agree. 2. Scripture, itself. Leviticus 5:4–6 says that if someone realizes he is guilty of a sinful rash vow, he can make atonement. It is better to acknowledge one's sin and deal with it than to continue on at the expense of others.