Unfaithfulness in marriage, often referred to as adultery, is a significant theme in the Bible, reflecting the sanctity and covenantal nature of the marital relationship. The Scriptures consistently portray marriage as a sacred union instituted by God, and any breach of this covenant is met with serious consequences.

Old Testament Context

In the Old Testament, the gravity of unfaithfulness in marriage is underscored by the Mosaic Law. Adultery is explicitly condemned in the Ten Commandments: "You shall not commit adultery" (Exodus 20:14). The law prescribed severe penalties for those who violated the marital covenant. Leviticus 20:10 states, "If a man commits adultery with another man's wife—if he commits adultery with his neighbor's wife—both the adulterer and the adulteress must surely be put to death" . This severe punishment highlights the seriousness with which God views marital fidelity.

The prophetic books often use the metaphor of marital unfaithfulness to describe Israel's spiritual adultery against God. The book of Hosea, for instance, portrays Israel as an unfaithful spouse, and God's judgment against such unfaithfulness is vividly depicted. Hosea 2:2-13 describes the consequences of Israel's infidelity, using the imagery of a broken marriage to illustrate the nation's betrayal of God.

New Testament Teachings

In the New Testament, Jesus reaffirms the sanctity of marriage and the sinfulness of adultery. In the Sermon on the Mount, He expands the understanding of adultery beyond physical acts to include lustful thoughts: "But I tell you that anyone who looks at a woman to lust after her has already committed adultery with her in his heart" (Matthew 5:28). This teaching emphasizes the importance of purity not only in actions but also in thoughts.

Jesus also addresses the issue of divorce, which is often linked to marital unfaithfulness. In Matthew 19:9, He states, "And I tell you that whoever divorces his wife, except for sexual immorality, and marries another woman, commits adultery" . This passage underscores the seriousness of marital vows and the limited grounds for divorce, highlighting sexual immorality as a breach of the marital covenant.

The Apostle Paul further elaborates on the sanctity of marriage in his epistles. In 1 Corinthians 6:9-10, he lists adulterers among those who will not inherit the kingdom of God, emphasizing the spiritual consequences of such actions. Paul also calls for marital fidelity in Ephesians 5:22-33, where he compares the relationship between husband and wife to that of Christ and the Church, underscoring the depth of commitment and love required in marriage.

Spiritual Implications

The Bible presents unfaithfulness in marriage not only as a violation of a human covenant but also as a sin against God. Malachi 2:14-16 highlights God's role as a witness to the marriage covenant and His disdain for divorce and unfaithfulness. The prophet declares, "For I hate divorce, says the LORD, the God of Israel" (Malachi 2:16), indicating the divine perspective on the sanctity of marriage.

Throughout Scripture, the call to faithfulness in marriage is a reflection of God's own faithfulness to His people. The marital relationship serves as a metaphor for the covenant between God and His people, and unfaithfulness in marriage is seen as a parallel to spiritual unfaithfulness. The judgment against such actions serves as a reminder of the holiness and commitment required in both human and divine relationships.