Preachers really should talk about Leviticus, since it can cause great confusion and division among Christians.
Interpretations vary all the way from the Marcionate/Bultmannian dismissal of the whole Old Testament, to Luther's (in)famous pronouncement: "Moses is dead. His rule ended when Christ came. He is of no further service,"1 to the direct and literal application of Levitical law on the part of some Christian groups (though, even then, few would include, say, the sacrificial regulations as a present requirement). So, what is a preacher to do? Even more, what is a parishioner to do?
Jesus will help us here! When he pronounces "You shall love your neighbor as yourself" to be the second greatest commandment in this week's Gospel (Matthew 22:39; see Leviticus 19:18), he sets up a canon within the canon that marks his own faith and shapes ours forever. Had he chosen, perhaps, "You shall not ... tattoo any marks upon you" (Leviticus 19:28) as the second commandment, we would be in an entirely different religion (and we would have a lot fewer young adults in church). Still, how are we to understand a book where "no tattoos" stands as a "thou shalt not" just ten verses away from "love your neighbor" as a "thou shalt"?
If we are to preach on this text, we should preach on Leviticus. That is, our sermon should not be the same as one on Matthew 22. Leviticus is about holiness: God's holiness and the holiness of God's people. "Holy" appears in Leviticus far more frequently than in any other biblical book. Because of this concentration, scholars have often called Leviticus 17-26 the "Holiness Code," understanding it as a separate source within Israel's legal traditions.
If you speak of this, however, beware of how you use the term "code," for you don't want to feed the "Da Vinci Code" madness that understands the Bible, or parts thereof, to be encrypted, requiring some kind of "magic" key to decipher. Remember that Leviticus -- indeed, the whole Bible -- decries and forbids magic (Leviticus 19:31). Happily, the Bible is an open WYSIWYG book, that is, "what you see is what you get."
The "key" to understanding Leviticus's emphasis on holiness is not hidden: human holiness, Leviticus insists, derives from God's holiness. "You shall be holy, for I the Lord your God am holy" (19:2). Levitical holiness (or biblical holiness), then, is not a human attribute to be obtained through our own righteousness (and surely not a "holier than thou" perspective); it is a divine gift, in which we partake of God's own holiness, just as humans partake of God's own image. "You shall be holy," like so many of the Old Testament apodictic laws, can also be read as promise: "Because I am holy, you will be holy. It is my gift to you. It is who you are."
What will this holiness look like? On the one hand, God is holy because God is Other, and this divine holiness makes God dangerous. Don't come too close, lest you die (see 2 Samuel 6:6-7).
Holiness is not wrath or caprice; it is not, "Don't come near or I will kill you." Holiness is inherent in the nature of God. Think, God as blast furnace. Don't draw near! The furnace kills not because it is angry, but merely because it is hot. This clear understanding that God is God, and we are not, is why Israel was given or developed the elaborate laws of purity and sacrifice, with which Leviticus is rife, in order precisely to allow people to come into God's presence (which God desires) without danger.
If holiness is in God's nature, however, it is important to understand that nature. Leviticus 19 begins with a call to be holy, for "I the Lord your God am holy," and it ends (an inclusio) by telling us what this means: "I am the Lord your God, who brought you out of the land of Egypt" (19:36). True, God is Other simply because God is God, but -- perhaps even more important for biblical theology -- God is Other because God liberates captives, sets people free, stands opposed to tyrants and oppressors (the preacher might extend this to the oppressors within us as well as those outside ourselves).
Isaiah makes this clear: God, the "Holy One of Israel," redeems Israel (frees from captivity), because -- surprisingly, for a God who is Other -- "I love you" (Isaiah 43:3-4). This same divine nature informs our chapter of Leviticus, with its insistence that Israel (because it mirrors God's own holiness) should reserve food for the poor and the alien (19:10), not defraud others or withhold fair wages (verse 13), care for the blind (verse 14), not show partiality in law (verse 15), not hate or take vengeance (verse 18), care for the aged (verse 32), not cheat (verses 35-36), and--again, surprisingly, for a people who understood itself to be uniquely the people of God -- love not only the neighbor but also the alien as oneself (verse 34). Observing such laws in virtually any human society will mark a people as other, partaking of the otherness of a remarkable God.
This love for the other is the "key" that unlocks the strangeness of Leviticus for modern readers. The early Jewish rabbis understood this clearly, which is why they, like Jesus, saw this verse as the most basic law in the Old Testament. Jesus stands firmly in this tradition. Any form of religion that belittles the other for the sake of self will get Leviticus wrong and get Jesus wrong. Any legalism that binds people in the name of religion rather than setting them free will get Leviticus wrong and get Jesus wrong.
The New Testament does not erase the otherness of God, nor does it invent the command to love. It does, however, provide different access to this dangerous God than the purity laws of ancient Israel. Now, access is given through Jesus, God's own son, who becomes the door or gateway into the divine presence, into the divine Love that embraces all -- ourselves, our neighbors, and any we might understand to be "aliens."
1See Luther's 1525 sermon on "How Christians Should Regard Moses," in Luther's Works, vol. 35 (Philadelphia: Muhlenberg, 1960), 165.