The biblical definition of adultery is far more expansive and complex than the modern, secular understanding of marital infidelity. The concept is rooted in the idea of a sacred covenant, viewing marriage not merely as a legal contract but as a divine bond. Adultery is understood as a profound violation of this covenant between two people and a sin against God himself. This framework establishes a standard of faithfulness that extends beyond the physical act to encompass internal thoughts and spiritual devotion. The Bible presents a progression of understanding, beginning with a strict legal definition and expanding to include the inner life and metaphorical unfaithfulness.
The Original Old Testament Definition
The foundational definition of adultery is established in the Mosaic Law, specifically in the Seventh Commandment: “You shall not commit adultery” (Exodus 20:14). In the Old Testament context, the Hebrew term for adultery, na’aph, referred strictly to sexual intercourse involving a married person and someone other than their spouse. This act was considered a grave offense because it violated the marriage covenant and infringed upon the husband’s rights within the patriarchal society.
The severity of the offense is demonstrated by the prescribed punishment under the law. Leviticus 20:10 states that both the adulterer and the adulteress were to be put to death. This penalty underscores the seriousness with which the community viewed the breach of the marital bond, which was seen as a threat to the social and religious order.
It is important to distinguish adultery from fornication. Adultery (moicheia in Greek) specifically involves the violation of a marriage vow by one or both parties. Fornication (porneia in Greek) is a broader term that refers to any sexual relations outside of the marriage covenant, such as sex between two unmarried people.
The Old Testament definition focused on the physical act that broke the established covenant. This legalistic framework provided a clear, external boundary for acceptable behavior within the community. The focus remained on the observable action and its consequences for the marriage.
Adultery of the Heart
The New Testament introduced an expansion of the definition of adultery through the teachings of Jesus. In the Sermon on the Mount, Jesus shifted the focus from the external act to the internal intention and thought life. He stated that anyone who looks at a person with lustful intent has already committed “adultery in the heart” (Matthew 5:28).
This teaching redefined the scope of the sin, suggesting that the violation begins in the mind before it manifests in physical action. Jesus pointed out that the attitude and desire are equally sinful. The sin is rooted in the volitional choice to dwell on inappropriate desire, moving beyond simple attraction to a deliberate fantasy or intent.
The implication of this higher standard is that personal purity is a matter of the heart, not just outward compliance with the law. Jesus’s statement challenged the legalistic mindset, suggesting that the thoughts themselves could be sinful on the same level as the physical act.
This internal standard applies to all followers, demanding a commitment to purity and devotion that governs one’s inner life. The teaching highlights that the true measure of righteousness is not merely what a person does, but what they think and feel.
Divorce Remarriage and Adultery
A complex dimension of the biblical definition concerns the relationship between divorce, remarriage, and adultery. Jesus taught that dissolving a marriage and subsequently marrying another person can constitute adultery, emphasizing the lifelong nature of the marriage covenant. This teaching is recorded in passages such as Matthew 19:9, Mark 10:11-12, and Luke 16:18.
The core concept is that marriage is a permanent union. An unscriptural divorce does not truly dissolve the bond in God’s view. Therefore, entering a new marriage while the first spouse is still living is seen as a continuation of the original covenant violation, making the second union adulterous.
Matthew 19:9 includes a specific allowance, often called the “exception clause,” which states that divorce and remarriage are permissible only in the case of porneia, or sexual immorality. The Greek term porneia is a broad word that encompasses various forms of sexual sin, including adultery, prostitution, and incest. This clause suggests that if the marriage covenant is already broken by a spouse’s sexual misconduct, the innocent party is permitted to divorce and remarry without committing adultery.
The interpretation of porneia remains a subject of theological discussion. Regardless of the specific interpretation, the teaching establishes that only a profound breach of sexual faithfulness provides grounds for dissolution without the subsequent remarriage being considered adulterous. The focus here is on the legal and covenantal status of the marriage itself.
Spiritual Adultery and Idolatry
Beyond the literal and internal definitions, the Bible frequently uses “adultery” in a metaphorical sense to describe spiritual unfaithfulness. This concept is primarily found in the Old Testament prophetic books, such as Hosea, Jeremiah, and Ezekiel. In this context, God is consistently portrayed as the faithful husband, and Israel or the Church is represented as the unfaithful wife.
Spiritual adultery is defined as idolatry, the act of turning away from the exclusive worship of God to pursue other gods or worldly things. The prophets used the imagery of a wife abandoning her husband for other lovers to illustrate Israel’s covenant-breaking with God. This unfaithfulness was often manifested through the adoption of pagan religious practices.
The metaphor emphasizes that God demands exclusive loyalty. Breaking the First Commandment (“You shall have no other gods before Me”) is equivalent to marital infidelity. The spiritual dimension of adultery highlights that the covenant relationship with God is personal and intimate, mirroring the bond of marriage. Any divided affection or devotion to worldly pursuits is seen as a betrayal of that sacred relationship.