Problem with Legalism

My problem with legalism is that it can't produce a pure heart. Rules do not protect us from sin because rules are basically guidelines that will help you avoid sinning. Jesus had a problem with the pharisees who were very legalists and they had about 613 rules to protect God's commandments. To me: Legalism is from the Law while Grace is from the Heart. Rules can be abused: Matthew 23:1-4 and Galatians 6:12-13. We are under Grace and that we are to obey God and follow His Word (the Bible). God wants a pure heart from us and He does not need to give us rules in order for our hearts to be pure. Jesus Christ cleaned our sins and all God wants us to do is be Christ-like. Jesus said in Matthew 5:8 "God blesses those whose hearts are pure, for they will see God." God wants our hearts more than He want us to follow rules. If we give our hearts to God, then we will know what is sinful and what is not sinful.