These are the statutes and rules and laws that the LORD made between himself and the people of Israel through Moses on Mount Sinai. - Leviticus 26:46 (ESV)
Leviticus is perhaps the most underrated book of the Bible. Despite its importance, it is often considered difficult to read and even more difficult to derive any benefit. I hope to contribute to changing that perspective.
I consider the big idea of Leviticus to be that God's presence demands his people's holiness. From the beginning to the end of Leviticus, the overarching thrust is the instructions God gives for his people to be holy and set apart, devoted to him. The passage above is representative of that fact.
An Outline of Leviticus
The first 7 chapters of Leviticus outline the types of offerings or sacrifices to God and how to make them. These chapters describe which kinds of animals may be sacrificed. They also describe different sorts of offerings of produce. The kinds of offerings mentioned and prescribed are the burnt, grain, sin, guilt, ordination, and peace offerings.
Chapters 8-10 of Leviticus handle the consecration of Aaron and his sons to the priestly ministry. 3 offerings are made for this occasion: a sin offering, a burnt offering, and an ordination offering. The next day, more offerings are made. At the end, when all the ceremonies were over, chapter 9 tells us that the glory of the Lord appeared to everyone and fire came out to consume what was left of the offerings. Chapter 10 is, sadly, a grim comedy of errors. Aaron's sons, Nadab and Abihu, offer unauthorized fire to Yahweh. Yahweh consumes them with fire in response. Subsequently, Aaron's other sons, Eleazar and Ithamar, neglect to eat a portion of the sin offering that they ought to have eaten. Moses becomes angry, but Aaron reasons with him and all is ok.
Chapters 11-15 treat the issue of cleanness and uncleanness. This section covers animals that are clean or unclean to eat. It also covers various physical issues people may have, some of them diseases and others not. There is also a discussion of homes and what to do with different kinds of growth and rot.
Leviticus Chapter 16 is one of the most important chapters of the Bible. It describes the Day of Atonement, during which the High Priest enters the Most Holy Place, the innermost room of the Tabernacle or Temple where the Mercy Seat is kept, to offer incense and the blood of animals as atonement for the uncleanness and transgressions of God's people. Hebrews makes a direct connection between the Day of Atonement and the work of Christ on the cross. This connection in Hebrews is worth quoting in full:
 But when Christ appeared as a high priest of the good things that have come, then through the greater and more perfect tent (not made with hands, that is, not of this creation)  he entered once for all into the holy places, not by means of the blood of goats and calves but by means of his own blood, thus securing an eternal redemption.  For if the blood of goats and bulls, and the sprinkling of defiled persons with the ashes of a heifer, sanctify for the purification of the flesh,  how much more will the blood of Christ, who through the eternal Spirit offered himself without blemish to God, purify our conscience from dead works to serve the living God.  Therefore he is the mediator of a new covenant, so that those who are called may receive the promised eternal inheritance, since a death has occurred that redeems them from the transgressions committed under the first covenant. - Hebrews 9:11–15 (ESV)
It is impossible to overstate the importance of the Day of Atonement for the work of Christ and our salvation. This is how God established a means by which a sacrifice could be made that would take away sins forever and not just temporarily. Thus the key to Christ's work is described in perhaps the least likely of all places for many people: the book of Leviticus.
Chapters 17 through 22 cover various laws for regulating life among God's people. The laws range from sacrifices to purity, from justice to idolatry, and from incest to witchcraft. Many of the laws begin with something like the phrase, "If anyone...". This is what is known as casuistry, the determination of what to do in specific cases. There are of course far too many possibilities to describe, but these are intended to serve as a broad enough range of examples for future leaders to be able to discern the way forward in almost any case.
Chapters 23 through 25 cover the Israelite feast days and the Year of Jubilee, intended to serve as a blank slate for all sorts of financial and property issues, including the enslavement of fellow Israelites to pay debts.
Chapter 26 is, along with Deuteronomy 28, one of the most helpful chapters for understanding the rest of the Old Testament. This is because Leviticus 26 outlines the blessings and curses for keeping or breaking the covenant. The rest of the Old Testament may be read in the light of this chapter. God does in Joshua through Malachi precisely what he says he will do in Leviticus 26.
27 Vows Leviticus ends in chapter 27 with a discussion of vows and valuations. This is intended to help the priests know how to manage the connection between finance and worship for God's people, ensuring just prices and proper treatment of different materials, animals, and property related to worship.
The Benefits of Leviticus
What is Leviticus good for? Much in every way. Leviticus is God's blueprint for a society devoted to him. It is a set of master plans for all people to know and especially for the Levites to implement. Sadly, we hardly see at any point what life in Israel is like with this law being fully followed.
We might ask, "Why would God give this law with all these instructions only for most of it to seem to be ignored?" It is a fair question. If we consider what happens in the rest of the Bible, however, the importance and usefulness of Leviticus become clear: the rest of the Bible occurs in the shadow of Leviticus. The Israelites' lack of conformity to the law does not undermine the importance of Leviticus but highlights it. The fact that the Israelites do not live up to the law dominates the rest of the Old Testament and carries us right into the New Testament, to the gracious and law-affirming words of Christ.
Leviticus is also a huge help in preparing us to understand and appreciate the work of Christ. As heavy, detailed, and burdensome as the law in Leviticus is, the God who gave them became one of us to fulfill them when we couldn't. Not only that, but Christ also served as the sacrifices offered for sin and on the Day of Atonement to atone for our guilt, pay for our sin, and make peace with God.
Christ does not invalidate the law. He fulfills it. And as we live today, we do not live in a world completely separated from the law of Leviticus as though it had nothing to do with us. We still live in the shadow of Leviticus, but we live as those who are no longer under its power because we follow Christ who fulfilled the entire law for us. And so as we read Leviticus, we can read not with boredom and confusion, but with a sense of awe and wonder at the great work our Savior accomplished for us. God's presence demands his people's holiness. But that holiness is something provided for us and performed upon us by God and not something that we achieve by our own effort. And as those who have been set apart by God for God, we pursue holiness as participants in the new covenant, not as a means of salvation but as a fruit of it.