The rest of the Old Testament deals specifically with God's chosen people, the descendants of Abraham. God revealed His law for the chosen people, for the most part, through Moses. You will find law throughout the Old Testament, but it is grounded solidly in the Mosaic Law. Some of these rules rest firmly on the 10 Commandments and help us understand the fuller implication of those commandments. According to Colossians 2, Christians are not obligated to observe any of the ceremonial or civil rules.
Christians are, however, to obey the laws of proper governmental structures.
It is no wonder that people get confused. According to Paul's argument in Romans 1-5, there are two ways to be saved. One way is to keep the law perfectly. If you could live and never violate any of God's law or your own conscience, God would owe you salvation because you deserve it. Sin is the transgression of law.