While Genesis emphasizes the great subject of life in its beginnings, and Exodus considers God's principles of redemption and His authority established among a redeemed people, Leviticus (named for Levi, meaning "joined") is the book of the sanctuary. Here we are brought into the very presence of God, so that sanctification to God and from all evil is the proper character of His saints.
Sanctification has two major aspects. First, sanctification by the one offering of Christ (Hebrews 10:10), which is God's work for us, putting the believer in a new position before God; the other, sanctification by the Spirit of God (1 Corinthians 6:11), which is God's work inwardly in the believer, causing him to be morally set apart to God. Both of these are implied in Leviticus.
Only on the basis of the sacrifice of Christ are we privileged to enter God's presence; therefore Leviticus begins with the various aspects of the value of that one great sacrifice. In all of this the Holiness and truth of God are specially prominent, just as in Genesis His power and majesty are displayed, and in Exodus His righteousness and grace.