Biblical Definition Of
The teaching of the Bible is that sexual relations are lawful only between husband and wife. A sexual relation between two people who are not married is usually called fornication; a sexual relation between a married person and someone other than that person’s marriage partner is usually called adultery (Exod 20:14; Rom 12:9,20; Gal 5:19; 1 Thess 4:3-4).
Old Testament regulations
According to the law of Moses, the punishment for adultery was death by stoning (Lev 20:10; John 8:3-5). Where there was a suspicion of adultery but no clear evidence, Israelite law set out a special procedure by which a priest could determine the case (Num 5:11-31). The engaged as well as the married were considered adulterers if they had sexual relations with third parties. Again the penalty was death. The one exception was the case of a woman who had been raped (Deut 22:22-27).
Adultery was a sin against one’s own marriage partner (Mal 2:11,14; cf. Hosea 2:2), as well as against the marriage partner of the new lover (Exod 20:14,17; 2 Sam 12:9; Prov 6:32-35). Unfaithfulness was at the centre of all adultery. The Old Testament prophets repeatedly spoke of Israel’s unfaithfulness to God as spiritual adultery, or spiritual prostitution (Jer 5:7; 23:10; Ezek 16:30-38; 23:4-5,11; Hosea 9:1).
New Testament teachings
Like the Old Testament, the New Testament looks upon marriage as a permanent union. Therefore, the person who divorced and remarried was considered guilty of adultery (Mark 10:2-12; Luke 16:18; Rom 7:2-4). The exception that Jesus allowed concerned the case where persistent adulterous behaviour by one partner had already virtually destroyed the marriage (Matt 5:32; 19:7-9). Jesus said that even the desire to have unlawful sexual relations was a form of adultery. Therefore, the best way to avoid adulterous acts was to avoid adulterous thoughts (Matt 5:27-30; 15:19; cf. Exod 20:17; James 1:14-15).
Paul pointed out that Christians in particular should avoid all immoral sexual relations, since their bodies are indwelt by the Holy Spirit and they themselves belong to Christ. For the Christian, there is a sense in which sexual sin is spiritual prostitution (1 Cor 6:13-20). Although the New Testament announces God’s judgment on those who are immoral and adulterous (Heb 13:4; 2 Peter 2:14), it also shows that God is ready to forgive those who, in sorrow for their sin, turn to him for mercy (1 Cor 6:9-11). Jesus rebuked the self-righteous who condemned adulterers but who could not see their own sin. At the same time he gave sympathetic support to those who acknowledged their sin and repented of it (Matt 9:11-13; Luke 18:9-14; John 8:3-11; cf. Rom 2:22).
Christians may rightly condemn adultery, but, remembering their own weaknesses, they should also forgive those who repent of their adultery. More than that, they should give them understanding and support as they try to re-establish their lives (2 Cor 2:7; Gal 6:1-2; Eph 1:7; 4:32).