You shall be holy, for I the Lord your God am holy.
The book of Leviticus is full of lessons — God was teaching his people how he wanted them to live. The people God was teaching lived in a world where they were surrounded by different tribes most of whom worshipped idols which led to evil and cruel behaviour. God was determined his people should be different because God himself was different - "You shall be holy, for I the Lord your God am holy".
What did this mean? God is the great example of what holiness means. In his case (God is in a class by himself) it means absolute purity; God is high above us, separate from sin and everything unclean; he is pure perfection!
So what does this mean for me if I am one of his people? Think of the sun shining down on a bright object. The sun's light is reflected and it can brighten up other objects that may be in the dark. So God's people have to reflect God's likeness — they have to have shining lives of purity, morally clean in heart and life — in other words they have to be holy for God is holy. This can be very hard in a society that may hate the things of God a society in which immorality, dishonesty, and lack of integrity comes to be acceptable. Chapter 19 of Leviticus is a very practical chapter of godly living and neighbourly love — holiness in action.
Dear Lord, sometimes I feel very unholy. Cleanse me and keep me pure in heart and life. Amen.