Adultery, defined as voluntary sexual intercourse between a married person and someone who is not their spouse, is addressed with significant gravity in the Bible. The Scriptures consistently portray adultery as a serious sin, warranting severe consequences both spiritually and, in some instances, physically.

Old Testament Law

In the Old Testament, the Mosaic Law explicitly prescribes the death penalty for adultery. Leviticus 20:10 states, "If a man commits adultery with another man's wife—with the wife of his neighbor—both the adulterer and the adulteress must surely be put to death." This severe punishment underscores the sanctity of marriage and the seriousness with which God views the violation of the marital covenant.

Deuteronomy 22:22 further reinforces this command: "If a man is found lying with a married woman, both the man who lay with her and the woman must die. You must purge the evil from Israel." The communal aspect of this law highlights the broader social and spiritual implications of adultery, emphasizing the need to maintain purity within the community of God's people.

Prophetic Writings

The prophets frequently use the metaphor of adultery to describe Israel's unfaithfulness to God. In Jeremiah 3:8-9, God speaks of Israel's spiritual adultery: "Because faithless Israel had committed adultery, I gave her a certificate of divorce and sent her away. Yet her treacherous sister Judah was not afraid; she also went and prostituted herself." This metaphorical use of adultery illustrates the gravity of idolatry and covenant unfaithfulness, equating spiritual infidelity with the physical act of adultery.

New Testament Teachings

In the New Testament, Jesus addresses the issue of adultery with a focus on the heart's intentions. In Matthew 5:27-28, He expands the understanding of adultery beyond the physical act: "You have heard that it was said, 'Do not commit adultery.' But I tell you that anyone who looks at a woman to lust after her has already committed adultery with her in his heart." This teaching emphasizes the internal nature of sin and the need for purity of heart.

While the New Testament does not prescribe the death penalty for adultery, it maintains the seriousness of the sin. In John 8:3-11, the account of the woman caught in adultery demonstrates Jesus' approach to sin and forgiveness. Although the law demanded her death, Jesus offers mercy, instructing her to "go and sin no more" (John 8:11). This incident highlights the balance of justice and grace, emphasizing repentance and transformation.

Apostolic Writings

The apostolic writings continue to affirm the sinfulness of adultery. In 1 Corinthians 6:9-10, Paul lists adulterers among those who will not inherit the kingdom of God: "Do you not know that the wicked will not inherit the kingdom of God? Do not be deceived: Neither the sexually immoral, nor idolaters, nor adulterers, nor men who submit to or perform homosexual acts... will inherit the kingdom of God." This warning serves as a call to holiness and a reminder of the eternal consequences of unrepentant sin.

Conclusion

The Bible consistently portrays adultery as a grave sin with serious consequences. From the death penalty in the Old Testament to the call for repentance and purity in the New Testament, the Scriptures emphasize the sanctity of marriage and the need for faithfulness. Adultery is not only a violation of the marital covenant but also a sin against God, requiring sincere repentance and a commitment to righteousness.John 8:3-11
And the scribes and Pharisees brought to him a woman taken in adultery; and when they had set her in the middle,
Topicalbible.org

Whether it is Lawful for a Man to Kill his Wife if She be ...
... Since then the just punishment of adultery is death, because it is a capital sin,
it would seem lawful for a husband to kill his adulterous wife. ...
/.../christianbookshelf.org/aquinas/summa theologica/whether it is lawful for 21.htm

Whether in a Case of Divorce Husband and Wife Should be Judged on ...
... for divorce in both. For divorce is a punishment of adultery, in so far
as it is opposed to the marriage goods. Now as regards the ...
//christianbookshelf.org/aquinas/summa theologica/whether in a case of.htm

Reformation of Abuses at Rome by the Emperor Theodosius.
... Antiq., art. Sistrum. [749] From a law of Constantine's (Cod. 9. 30) whose genuineness
is, however, disputed, the punishment of adultery was death. ...
/.../chapter xviii reformation of abuses at.htm

About the Young Man who Killed the Maiden.
... labouring and working; [2387] and let the adulterers no more commit adultery, lest
they give themselves up to everlasting punishment; for adultery is with God ...
/.../unknown/acts of the holy apostle thomas/about the young man who.htm

Spiritual Adultery.
... dissolution of the body; even as, among men, she who is caught in adultery is first
cast out from the house, and then afterwards is condemned to punishment.". ...
/.../unknown/the clementine homilies/chapter xxviii spiritual adultery.htm

The Woman Taken in Adultery.
... that sayest a man should not commit adultery, dost thou commit adultery?" but also ...
is due to this sin, and then to accept such proportionate punishment as would ...
/.../the expositors bible the gospel of st john vol i/xvii the woman taken in.htm

Deuteronomy
... neighbourliness, the protection of mother-birds, the duty of taking precautions
in building, the rights of a husband, the punishment of adultery and seduction ...
/.../mcfadyen/introduction to the old testament/deuteronomy.htm

Letter ccxvii. To Amphilochius, the Canons.
... The union of kindred within the prohibited degrees of marriage, if detected as having
taken place in acts of sin, shall receive the punishment of adultery. ...
/.../basil/basil letters and select works/letter ccxvii to amphilochius the.htm

David not Lustful, Though He Fell into Adultery.
... shown this, and God's punishment had been denounced against him, he wiped out his
sin in deep penitence. But yet in this parable it was the adultery only that ...
/.../on christian doctrine in four books /chapter 21 david not lustful though.htm

Whether the Division of Sins According to their Debt of Punishment ...
... Ex genere," genus in this case denoting the species], as murder and adultery; and
some ... in relation to its reward, so does sin stand in relation to punishment. ...
/.../aquinas/summa theologica/whether the division of sins.htm

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