God gives moral laws in the Bible for three reasons. The first is to steer the conscience of a society. Communities who are ignorant of God's moral law run amok more so than otherwise. The second is to drive the conscience to Christ. God the Holy Spirit uses our knowledge of moral law2 to convict us of our sins, and convince us of our need for forgiveness.
Jack is the teaching elder of Ironworks Pike Community Church. He is a graduate of Columbia Biblical Seminary http://www.ciu.edu.