Leviticus (Va’yikra in Hebrew) means “and He called”, which is how verse one starts. We call this book Leviticus because it records the duties of the Levites. The Hebrew title is representative of the content and purpose of the book, namely the calling of God’s people, and in particular the calling of the Levites, to minister before Him.
This book was written by Moses and its major themes are like an instruction manual for morals and ethics. There are civil, sanitary, ceremonial, moral and religious regulations for the nation of Israel. There are also instructions for making offerings (burnt, meat, peace, sin, trespass, grain). We have the ordination of Aaron and his son, rules and laws for purification, regulations for atonement, rules for sexual relationships, provisions for festivals, and final instructions and warnings.
All the offerings, as well as the ceremonies and laws, served to constantly remind Israel that God is eminently holy. God could be approached only by the priests, and then only in strict obedience to the detailed instructions for purification. God required the sacrifice of innocent animals for the covering of man’s sin. These sacrifices were symbolic of the ultimate sacrifice which would take away the sin of the whole world.
What’s really interesting is that in Leviticus you'll find some “divine warnings”. There will be terror, the people will be slain and others will be scattered. There are very specific points made in regards to bread and famine, waste and desolation.
Leviticus is clearly a manual for the priests to follow. It explains burnt offerings, grain offerings, fellowship offerings, sin and guilt offerings and how it is forbidden to eat fat and blood. The section on clean and unclean food (chapter 11) makes sense from a scientific point of view as well. As do the chapters (13, 14) about infectious skin diseases and dealing with mildew (mold). Chapter 18 gets uncomfortably specific (for some people) about sexual relations. “Do not have sexual relations” with a relative, someone of the same sex, or an animal, is pretty explicit and unambiguous; these statements cannot be argued away. God says “NO”, so don't do it.
Though the Ten Commandments were covered in Exodus 20, they appear again here in Leviticus 19 with some embellishments.
(Taken from Crossing the Scriptures)