Lev. 18, Unlawful relations

It is not until Leviticus 18 that, for the first time in the Bible, and probably in the history of man, sexual relationships with close relatives were banned. Whereas Abram had married his half-sister, Sarai, this type of marriage was now specifically forbidden.

Had Abraham then actually sinned?

No. This is where biology comes in. Adam and Eve were created without any faults, or mutations, in their genetics. However, through time, mutations accumulate in any species. This is called "genetic load." Most detrimental mutations which survive in a population are kept pretty well hidden because they are recessive. This means that if the mate does not have that same mutation, then the genetics of the mate is dominant and the genetics of the carrier of the bad mutation is weaker in that one area. However, if two people who have the same negative mutation marry and have a child, there is a good chance this child will not just carry that mutation, but that its negative effects will be shown in the child. These are birth defects.

Until the time of Moses, there were not enough mutations that had built up in humans to cause a problem. But by his time there were. So marrying outside the immediate family now becomes a necessity and the Lord establishes the boundaries for lawful sexual relations.

The laws about sexual relations that we find in this chapter can be covered pretty completely in just a few general sentences, the first being a quote from Hebrews 13:4:

1. Marriage should be honored by all, and the marriage bed kept pure, for God will judge the adulterer and all the sexually immoral.

2. No sexual relationship with a close relative or during a woman's monthly period.

3. No sexual perversions, of which homosexuality is specified as one here.

In the middle of the laws regarding sex there is one that seems out of place, in verse 21:

Do not give any of your children to be sacrificed to Molech, for you must not profane the name of your God. I am the Lord.

Why is this stuck in the middle of the laws on sex?

First of all, a natural result of sex is children. And children are a gift from the Lord, for He is in charge of life itself. No child is an accident. No conception is outside of God's will. Thus, sacrificing children is not only denying one of the reasons for sex, but is rejecting a gift from God. To add insult to injury, these sacrifices were being done to honor an idol.

This command regarding the children lies in between a law regarding adultery and some regarding sexual perversions, all of which are detestable to the Lord. Thus, the sacrificing of children was/is at least as abominable to the Lord as adultery or perverted sex. And, conversely, both adultery and perverted sex are as detestable to the Lord as the sacrifice of a child.