The Bible describes infidelity (usually called adultery or sexual immorality) as a serious sin that violates the marriage covenant, but it also emphasizes the possibilities of repentance, forgiveness, and, in some cases, divorce. It presents both firm moral boundaries and pathways for grace.

How the Bible defines infidelity

In Scripture, infidelity is primarily any sexual activity outside the covenant of marriage, whether physical or, in Jesus’ teaching, even willful lust in the heart. Jesus expands the seventh commandment (“You shall not commit adultery”) by teaching that looking at someone with lustful intent is already a form of adultery in the heart, showing that unfaithfulness begins internally before it becomes an outward act.

Moral seriousness and consequences

The Bible consistently treats adultery as a grave offense against both one’s spouse and God, describing it as self-destructive and a violation of God’s moral law. Old Testament laws for Israel even attached severe civil penalties to adultery, highlighting how seriously covenant-breaking was regarded in that context.

Grounds for divorce, not a command

Jesus affirms God’s design of lifelong, one-flesh union in marriage, but he acknowledges that sexual immorality can be a legitimate ground for divorce. At the same time, this is presented as a permission in light of human hardheartedness, not a command that divorce must happen whenever infidelity occurs.

Forgiveness and possible restoration

Alongside its strong condemnation of infidelity, the Bible also emphasizes God’s heart for mercy, repentance, and restoration. The prophetic story of Hosea and his unfaithful wife is used as a picture of God pursuing and restoring an unfaithful people, and Jesus’ response to the woman caught in adultery combines refusal to condemn her with a call to “sin no more,” pointing to both grace and change.

Spiritual infidelity to God

The Bible often uses marital unfaithfulness as a metaphor for spiritual unfaithfulness, describing worship of other gods or divided loyalty as “adultery” against the Lord. This language underscores that faithfulness in marriage mirrors the deeper covenant relationship between God and his people and that betrayal in either sphere is taken very seriously.

If you share more about whether you’re asking from a personal situation, for study, or for teaching, the key passages and applications can be tailored more specifically.