ANSWER: Strictly speaking, the word "incest" is not found anywhere in the King James Bible. The Old Testament, however, does define the types of people who are not to have sex with one another (and, by extension, are not allowed to marry each other).
The book of Leviticus is the primary place we find prohibitions that define what God considers incest. Chapter 18 specifically forbids sex (and marriage) between a man and their mother (or stepmother) or father, sister (or half-sister), daughter-in-law, granddaughter, aunt (by blood or marriage), or sister-in-law.
Verse 16 of Leviticus 18 forbids a man from having sex with his brother's wife. There is an Old Testament exception to this, however, in the case where a man's brother dies without a son. In such circumstances, the man was duty-bound to marry and have sex with his brother's widow (in order to produce at least one son) so that "his name may not be put out of Israel" (see Deuteronomy 25:5 - 10).
Verse 17 of Leviticus 18 declares it is incest for a man to have a sexual relationship with a woman and her daughter (a daughter from a previous relationship - a stepdaughter), either at the same time or with the daughter if the woman dies. It also forbids such a relationship with the daughter of either the woman's daughter or son (step-granddaughter). Verse 18 of the chapter prohibits taking a woman AND her sister as rival wives. This scripture would not apply today for places that already forbid polygamy.
The basic principle on which the laws against incest are founded is located in verse 6 of the chapter.
|6. None of you shall approach to any who are near of kin to him to uncover their nakedness (a Hebrew euphemism for having sex). I am the LORD (Leviticus 18:6, HBFV throughout)|
Interestingly, the Bible does not specifically forbid the marriage of cousins. However, because of 6,000 years of genetic mutations, the chance of passing on genetic defects to the children of such a union might make such a relationship unwise. Such marriages may also be illegal based on local or national laws. For example, in America, only about half the states allow first cousin marriages (some with restrictions).
Old Testament Examples
Scripture contains several examples of incest that was allowed (tolerated) before the giving of the law. For example, God allowed Adam and Eve's children to marry (and have sex with) each other, such as Cain and Seth having to marry one of their sisters. Close kin marriages, out of necessity since the human race was just starting, no doubt occurred for many years after our first parents were forced to leave Eden.
Lot, who was raised by his uncle Abraham, ultimately fled to the mountains, with his two daughters, after the destruction of Sodom and Gomorrah. His daughters got him drunk and committed incest with him (Genesis 19:30 - 38).
Abraham's grandson Jacob married Rachel and Leah, who were sisters. Their father Laban only allowed these marriages after he worked a total of fourteen years for him (see Genesis 29). The marriage of the sisters, though not codified as wrong until much later (Leviticus 18:18), nevertheless proved troublesome for Jacob (see Genesis 29 - 30).
New Testament Examples
John the Baptist condemned the marriage of Herod Antipas to his brother Philip's wife (Mark 6:17), an act that was clearly a sin (Leviticus 18:16, 20:21). His condemnation of Herod's incest got him put in prison and ultimately martyred (Matthew 14).
The apostle Paul had to grudgingly deal with a case of incest occurring in the church at Corinth. The church had a member who was having sex with his stepmother while his father was still alive! Rather than collectively condemning this behavior, the brethren shirked their responsibility and knowingly allowed it to continue. Paul had to step in and correct the situation by having the member thrown out of the fellowship until he repented (1Corinthians 5).
God's law enumerated differing penalties for those found committing incest. They included exclusion from the covenant people (Israel - Leviticus 18:29, 20:17 - 18), childlessness (Leviticus 20:20 - 21) or even death (Leviticus 20:11 - 12, 14). Amazing as it seems, however, God held people accountable for violating these and other basic principles of right and wrong (sinning) BEFORE he gave humans a codified copy of his law!
In Leviticus 18, after defining forms of incest, forbidding adultery (verse 20), human sacrifices (verse 21), homosexuality (verse 22) and bestiality (verse 23), the Eternal gives Israel a sobering warning.
24. Do not defile yourselves in ANY OF THESE THINGS, for in all these the nations which I cast out before you are defiled . . . Therefore I visit its wickedness against it, and the land itself vomits out those who live in it . . . 27. For the men of the land who were before you have done all these abominations, and the land is defiled (Leviticus 18:24 - 25, 27).
The Canaanites, or descendants of Canaan, had been living in the Promised Land since shortly after the great flood (Genesis 9:18, 13:7, etc.). Over time, their behavior became increasingly sinful and entrenched. Their punishment from God, for years of unacceptable behavior BEFORE the Commandments were given, was to have their land taken from them, given to the Israelites as an inheritance, and they be utterly destroyed (see Deuteronomy 7:1 - 2, Leviticus 20:22 - 24, etc.)!
God does not approve of sex with ANYONE, even if they are not closely related to you, outside the union of a husband and wife in matrimony. In fact, according to Jesus, even lusting after someone (before any physical act of incest could take place) is considered a sin (Matthew 5:28)!