How should we interpret Leviticus 18, 19?

You seem to be making an error, common to most people who read the Bible. And that this is error is that they do not comprehend exactly what is going on at the time the Pentateuch was written. The nation of Israel had been in slavery in Egypt for over 400 years. During that time they had gotten away from serving their God, and had been under the influence of a nation which served multiple god's.

Some of the Roman gods were immoral gods, and Egypt at the time was a very immoral country. After God delivered the nation Israel from slavery in Egypt, he had to retrain them and teach them his laws and his ways anew.

The book of Genesis was given to remind Israel of their history up to the time of Joseph which they no longer remembered. Beginning in the book of Exodus, For the most part throughout the second part of Exodus through the book of Deuteronomy, God is giving them his laws and rules for living. Although there is some overlap between the laws and the rules for living for the most part the laws are given as commands. Rules for living have to do with normal day to day life.

Beginning in Exodus chapter twenty verse 1 God gave the nation of Israel his basic laws.

(note) All Scriptures are quoted from the King James translation.

Exodus 20:1 through 17

1 And God spake all these words, saying,

2 I am the LORD thy God, which have brought thee out of the land of Egypt, out of the house of bondage.

3 Thou shalt have no other gods before me.

4 Thou shalt not make unto thee any graven image, or any likeness of any thing that is in heaven above, or that is in the earth beneath, or that is in the water under the earth:

5 Thou shalt not bow down thyself to them, nor serve them: for I the LORD thy God am a jealous God, visiting the iniquity of the fathers upon the children unto the third and fourth generation of them that hate me;

6 And shewing mercy unto thousands of them that love me, and keep my commandments.

7 Thou shalt not take the name of the LORD thy God in vain; for the LORD will not hold him guiltless that taketh his name in vain.

8 Remember the sabbath day, to keep it holy.

9 Six days shalt thou labour, and do all thy work:

10 But the seventh day is the sabbath of the LORD thy God: in it thou shalt not do any work, thou, nor thy son, nor thy daughter, thy manservant, nor thy maidservant, nor thy cattle, nor thy stranger that is within thy gates:

11 For in six days the LORD made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the LORD blessed the sabbath day, and hallowed it.

12 Honour thy father and thy mother: that thy days may be long upon the land which the LORD thy God giveth thee.

13 Thou shalt not kill.

14 Thou shalt not commit adultery.

15 Thou shalt not steal.

16 Thou shalt not bear false witness against thy neighbour.

17 Thou shalt not covet thy neighbour's house, thou shalt not covet thy neighbour's wife, nor his manservant, nor his maidservant, nor his ox, nor his ass, nor any thing that is thy neighbour's.

The same 10 Commandments are given again in Deuteronomy chapter 5, but some wording is changed in order to make it more understandable

Although these Commandments seems simple enough to us. It was difficult for the nation of Israel having been under the influence of the Egyptians for so many years to truly understand what that meant. For years under the Egyptian rule sexual promiscuity was the rule rather than the exception. What we find in the rest of the Pentateuch is God having to elaborate on the exact meaning of the 10 Commandments in order for the nation of Israel to understand.

In Leviticus, chapter 18 God is giving more explanation to his command that thou shalt not covet thy neighbor's wife, nor anything that is thy neighbor's. He is also telling them that h*m*sexuality and incest are against God's laws. In chapter 18 verses one through 30 God is defining unlawful marriage.(We must remember that in God eyes sexual intercourse constitutes Marriage.) In most religions that is known as consummating the marriage. We need only to look at the story of Joseph Leah, Rachel and their two maids beginning in Genesis chapter 29 to understand the permanence of that union in God's eyes. The children of all four comprises the nation of Israel.

In chapter 19 of Leviticus, we go to a completely different story, in Leviticus chapters 1 through 11 God is giving Israel a new set of commands about how he is to be served. He gives the rules for sacrifice. What animals are to be considered, clean and which are unclean, and he gives all of the instructions for the priest. What God is doing in chapter 19 is that after he has given them all of the laws and instructions on how to serve him; he is giving them a warning about not breaking these laws and instructions.

The laws which God gave always have and always will be in effect:

Matthew 5:17 and 18

Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfil. For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled.

The rules for worship that God gave to Israel. After bringing them out of Egypt do not apply to us, only in as much as we no longer have to sacrifice animals and we now have only one high priest which is Jesus Christ.

We are still bound by the law, even though Jesus fulfilled the law. Fulfilling the law is not the same as doing away with the law, every time that we break one of God's laws. It is one more sin that is piled onto Jesus at the cross. (I do not know if Jesus feels a new pain every time we sin, but it seems plausible to me that he would, or at least did at the cross.)

Remember what Jesus said to the woman caught in prostitution:

John 8:10 and 11

When Jesus had lifted up himself, and saw none but the woman, he said unto her, Woman, where are those thine accusers? hath no man condemned thee? She said, No man, And Jesus said unto her, Neither do I condemn thee: go, and sin no more.

Jesus told her to go and sin no more, he did not add "if you do after I go to the cross; it won't matter anymore."

By these Scriptures. We should understand that even though Jesus paid our sin debt in full. That does not mean the Law has been done away with. Thou shalt not commit adultery is just as cogent now as it was when Moses told the people of Israel coming out of Egypt.

There is much truth in the old saying that no sin goes unpunished.

How should we interpret Leviticus 18, 19?

One of the fundamental rules of Biblical Hermeneutics is to understand the audience being spoken to. In the case of Leviticus 18 & 19, the audience is the nation Israel.

It need not be commented on at length that only Israel was given the Law of Moses and, therefore, only Israel was subject to the Law of Moses. Gentiles (the foreskins, or the uncircumcision) is not obligated in any way to the rituals and practices of the system of ordinances. This is made clear by the Jerusalem Council (Acts 15) and the writings of the apostle Paul in romans chapters 3, 4, 5, 7 and 10. Justification (being declared righteous) in both the OT and Nt, is by faith, not by the works of the Law of Moses.

As curiousdannii pointed out in his comment above, Yeshua did not abolish the law, he fulfilled it. Concerning the fact of Yeshua’s fulfillment of the law (and the prophets), it need hardly be commented on at length that Yeshua kept the law. But the fulfillment of the Law goes far and beyond his keeping it.

The purpose of the law was to reveal God’s nature to sinful man; to make us aware of the things we do that are contrary to that nature, and to direct us to Yeshua. In other words, the law was given to make sin all the more sinful by making us aware of it. I believe it is in THIS sense that Yeshua is best seen as fulfilling the law. He did more than “keep” the law, he “fulfilled” its very purpose.

Wherefore the law was our schoolmaster to bring us unto Christ, that we might be justified by faith. But after that faith is come, we are no longer under a schoolmaster. —Galatians 3:24-25 (AV)

Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them. 18 For truly, I say to you, until heaven and earth pass away, not an iota, not a dot, will pass from the Law until all is accomplished. —Matthew 5:17-18 (AV)

The word “fulfill” in Matthew 5:17 means, “to accomplish the intended goal.” In verse 18 Yeshua says that nothing will go away until all is accomplished (fulfilled).

Therefore, Yeshua’s fulfillment of the law may best be stated as, “Yeshua accomplished all that was intended to be accomplished in the dispensing of the law to man.” But, there is more to it still.

Yeshua did not stop at fulfilling the law, at least not according to the author of Hebrews.

If therefore perfection were by the Levitical priesthood, (for under it the people received the law,) what further need was there that another priest should rise after the order of Melchisedec, and not be called after the order of Aaron? For the priesthood being changed, there is made of necessity a change also of the law. —Hebrews 7:11-12 (AV)

Yeshua is now our High Priest, not from the line (lineage) of Aaron and the Levites, but the new priesthood is after the order (manner) of Melchisedec. Now here is the really good part, the part that focuses on your question most pointedly—with this change in priesthood from the Levites to Melchisedec, there is a change, by necessity, in the law as well (Hebrews 7:12).

Leviticus 18 & 19 must be interpreted in the light of the new law. The old law was the law of sin and death. But the new law is the law of the Spirit of life.

For the law of the Spirit of life in Christ Jesus hath made me free from the law of sin and death. —Romans 8:2

Yeshua told us in Matthew—

Jesus said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind. 38 This is the first and great commandment. 39 And the second is like unto it, Thou shalt love thy neighbour as thyself. 40 On these two commandments hang all the law and the prophets. —Matthew 22:37-40 (AV)

Please observe that the two "new" commands of Messiah supersede ALL of the law and ALL of the prophets.

Paul, in the 14th chapter of Romans, talks about our liberty through faith in Messiah. That liberty is not to be used against those who have scruples of conscience. To paraphrase Paul's words— I believe I may eat pork if I so desire, but if I should find myself in the proximity of a brother who is clinging to Leviticus 18 for direction, then I must not eat pork in front of him and thereby damage his tender scruples. This is loving my neighbor as myself.

The Law of Moses served to make us aware of sin and to point us to Messiah. Yeshua fulfilled that law. He then moved on to a new priesthood and a new law. We must follow him.

The apostle wrote: “Christ hath redeemed us from the curse of the law” (Gal. 3,13). The main-stream view of Nicene Christians has been that Christ abolished only those parts of the Mosaic Law referring to circumcision, food regulations and the Sabbath, and that the rest of the Law remains valid, but there have been Christians (e.g. Marcion) who argue that Christ has abolished the Law in its entirety. Thus, from a hyper-Pauline antinomistic position you could argue that the whole of the Old Testament has no validity for Christians.

References: You could start by looking up “law” in any Biblical concordance, then the article νόμος in theThWbzNT. For Marcion there is the classic monograph by Harnack, Marcion, das Evangelium vom fremden Gott, 1920.