So far in our examination of relevant biblical law to maternal lines , we have seen restrictions that only applied to certain groups of people, specifically priests, kings, and female heirs. There were, however, some restrictions to marriage that were included for everyone. Perhaps surprisingly, these restrictions seem to have been based at least in part on the behavior of some of the patriarchs themselves. What was originally permissible no longer was permissible once God had seen the damages that had resulted from some of these misalliances, and once the risk of genetic damage for certain incestuous relationships became serious enough. Not only to these laws point to the past, though, but they also point to the future, in that these laws are cited in the New Testament as remaining in force for believers, and they have contemporary relevance concerning what sort of behavior is expressly forbidden to believers today regarding sex and marriage.
We find this general set of restrictions on marriage in Leviticus 18:1-30 (NIV). Let us quote the entire chapter and then comment on how it relates to the issue of maternal lines: “The Lord said to Moses, “Speak to the Israelites and say to them: ‘I am the Lord your God. You must not do as they do in Egypt, where you used to live, and you must not do as they do in the land of Canaan, where I am bringing you. Do not follow their practices. You must obey my laws and be careful to follow my decrees. I am the Lord your God. Keep my decrees and laws, for the person who obeys them will live by them. I am the Lord. No one is to approach any close relative to have sexual relations. I am the Lord. Do not dishonor your father by having sexual relations with your mother. She is your mother; do not have relations with her. Do not have sexual relations with your father’s wife; that would dishonor your father. Do not have sexual relations with your sister, either your father’s daughter or your mother’s daughter, whether she was born in the same home or elsewhere. Do not have sexual relations with your son’s daughter or your daughter’s daughter; that would dishonor you. Do not have sexual relations with the daughter of your father’s wife, born to your father; she is your sister. Do not have sexual relations with your father’s sister; she is your father’s close relative. Do not have sexual relations with your mother’s sister, because she is your mother’s close relative. Do not dishonor your father’s brother by approaching his wife to have sexual relations; she is your aunt. Do not have sexual relations with your daughter-in-law. She is your son’s wife; do not have relations with her. Do not have sexual relations with your brother’s wife; that would dishonor your brother. Do not have sexual relations with both a woman and her daughter.Do not have sexual relations with either her son’s daughter or her daughter’s daughter; they are her close relatives. That is wickedness. Do not take your wife’s sister as a rival wife and have sexual relations with her while your wife is living. Do not approach a woman to have sexual relations during the uncleanness of her monthly period. Do not have sexual relations with your neighbor’s wife and defile yourself with her. Do not give any of your children to be sacrificed to Molek, for you must not profane the name of your God. I am the Lord. Do not have sexual relations with a man as one does with a woman;that is detestable. Do not have sexual relations with an animal and defile yourself with it. A woman must not present herself to an animal to have sexual relations with it; that is a perversion. Do not defile yourselves in any of these ways, because this is how the nations that I am going to drive out before you became defiled. Even the land was defiled; so I punished it for its sin, and the land vomited out its inhabitants. But you must keep my decrees and my laws. The native-born and the foreigners residing among you must not do any of these detestable things, for all these things were done by the people who lived in the land before you, and the land became defiled. And if you defile the land, it will vomit you out as it vomited out the nations that were before you. Everyone who does any of these detestable things—such persons must be cut off from their people. Keep my requirements and do not follow any of the detestable customs that were practiced before you came and do not defile yourselves with them. I am the Lord your God.’””
These prohibitions are quite extensive. For our purposes, let us limit our discussion to those elements that are most relevant to our particular topic of descent through the female line. It should be noted that many of these restrictions against incest, which make up the majority of what is forbidden here, include relations by marriage as well as by blood. In the Bible, both of these relations make someone off limits. One cannot have any sort of legitimate sexual relations outside of marriage, and these groups of partners were declared off limits. At least two of the prohibitions, against bestiality and homosexuality, explicitly forced men to seek women for their partners in romance and intimacy, as opposed other potential options that remain problems even today among general society as well as those who profess to be believers. The role of these laws in restricting partners place a boundary around which kind of behaviors are unacceptable, and likely give a picture of the sorts of sins that people fell into in Canaan bringing upon divine judgment.
It should be noted that these laws remain in force for Christians today. This particular law, for example, is the only biblical law against bestiality. Additionally, this law was cited as part of Paul’s dealing with sexual immorality in 1 Corinthians 5:1-8: ”
It is actually reported that there is sexual immorality among you, and such sexual immorality as is not even named[a] among the Gentiles—that a man has his father’s wife! And you are puffed up, and have not rather mourned, that he who has done this deed might be taken away from among you. For I indeed, as absent in body but present in spirit, have already judged (as though I were present) him who has so done this deed. 4 In the name of our Lord Jesus Christ, when you are gathered together, along with my spirit, with the power of our Lord Jesus Christ, deliver such a one to Satan for the destruction of the flesh, that his spirit may be saved in the day of the Lord Jesus. Your glorying is not good. Do you not know that a little leaven leavens the whole lump? Therefore purge out the old leaven, that you may be a new lump, since you truly are unleavened. For indeed Christ, our Passover, was sacrificed for us. Therefore let us keep the feast, not with old leaven, nor with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth.” The situation Paul was dealing with is not like our own, where people glory in their toleration of that which God condemns. Let us also note the way that Paul ends his discussion in 1 Corinthians 5:13: “But those who are outside God judges. Therefore “put away from yourselves the evil person.”” The same punishment that God had for these sinners, putting them outside of the camp, is the disfellowshipment for these sins that Paul offers, showing the continuity between ancient Israel and the Church.
Let us look at least a little bit at how the behavior of the patriarchs themselves may have influenced some of these laws as well. At least two of these restrictions would have forbidden marriages from the patriarchs. Abraham, as we will see later, was married to his half-sister Sarah. Likewise, Jacob married two sisters who were rivals to each other, and it quite possible that their misery thanks to the deceit of their father moved God to forbid anyone else from repeating Jacob’s example of having two sister wives as rivals. In this way we can see that God’s law moved from permissive to more restrictive based on the behavior of people that let him know what sort of things needed to be explicitly forbidden. The law, in that way, works after abuses, in that the way that people act contrary to nature forces God to make laws more restrictive as time goes on. Incidentally, we may see this with regards to homosexuality, since male homosexuality is first noted and prohibited before lesbianism is condemned in Romans 1. Thus the law becomes even more strict in matters of morality as time goes on, something that we see as well in the Sermon on the Mount in the magnification of laws.
Summing it up, then, Leviticus 18 places restrictions around different kinds of sexual activity. Some of these laws prevent what is viewed as incestuous either by virtue of the bond of blood or marriage, which from what we can see is an equivalent bond according to scripture, forbidding intercourse with close relatives as well as stepsiblings and stepparents. Other laws restrict sexual conduct that is judged as unacceptable for everyone, including sex during menstration, bestiality, and homosexuality. In this way God affirmed the importance of the maternal line in several ways. For one, as relatives by marriage were counted as equal to marriages by blood, marriage was regarded as immensely honorable. For another, by prohibiting marriages or relations that put special stress on women–such as sisters or mother and daughter being made romantic rivals, the feelings of women were respected. For another, potential rivals to women in terms of intimate partners, like other men and or animals, were forbidden ,which would be a strong encouragement for men to marry in order to satisfy their sexual longings in a lawful manner. That was, after all, the intent.
 See, for example: