Definition and Context:
Spiritual adultery refers to the unfaithfulness of God's people when they turn away from Him to pursue other gods or worldly desires. This concept is frequently illustrated in the Bible through the metaphor of marital infidelity, where God is depicted as the faithful husband and His people as the unfaithful wife. Spiritual adultery is a grave sin as it signifies a breach of the covenant relationship between God and His people.

Biblical References:
The theme of spiritual adultery is prevalent throughout the Scriptures, particularly in the prophetic books. In the Book of Hosea, God commands the prophet to marry an unfaithful woman to symbolize Israel's unfaithfulness to Him. Hosea 1:2 states, "When the LORD first spoke through Hosea, He said to him, 'Go, take for yourself a wife of prostitution and children of unfaithfulness, because the land is committing blatant acts of prostitution by forsaking the LORD.'"

Jeremiah also addresses this issue, highlighting the betrayal of Judah and Israel. Jeremiah 3:20 declares, "But as a woman may betray her husband, so you have betrayed Me, O house of Israel,” declares the LORD."

In the New Testament, James warns believers against friendship with the world, equating it to spiritual adultery. James 4:4 admonishes, "You adulteresses! Do you not know that friendship with the world is hostility toward God? Therefore, whoever chooses to be a friend of the world renders himself an enemy of God."

Consequences of Spiritual Adultery:
The consequences of spiritual adultery are severe, as they involve both temporal and eternal ramifications. In the Old Testament, the unfaithfulness of Israel and Judah led to divine judgment, including exile and destruction. The Book of Ezekiel vividly describes the consequences of such infidelity. Ezekiel 16:38 warns, "And I will sentence you to the punishment of women who commit adultery and who shed blood, and bring upon you the wrath of bloodshed and jealousy."

The New Testament continues to emphasize the seriousness of spiritual adultery. In Revelation, the church in Ephesus is admonished for losing its first love, with a call to repentance to avoid removal of their lampstand. Revelation 2:4-5 states, "But I have this against you: You have abandoned your first love. Therefore, keep in mind how far you have fallen. Repent and perform the deeds you did at first. If you do not repent, I will come to you and remove your lampstand from its place."

The Call to Repentance:
Despite the grave consequences, the Bible consistently offers a path to restoration through repentance. God’s desire is for His people to return to Him with sincere hearts. In Hosea 14:1-2 , the call is clear: "Return, O Israel, to the LORD your God, for you have stumbled by your iniquity. Bring your confessions and return to the LORD. Say to Him, 'Forgive all our iniquity and accept what is good, so that we may repay You with the fruit of our lips.'"

The promise of forgiveness and restoration is a recurring theme, emphasizing God's enduring love and mercy. Joel 2:13 encourages, "Rend your hearts and not your garments. Return to the LORD your God, for He is gracious and compassionate, slow to anger, abounding in loving devotion. And He relents from sending disaster."

Conclusion:
Spiritual adultery is a profound betrayal of the covenant relationship with God, carrying significant consequences. However, the consistent biblical message is one of hope and redemption through genuine repentance and a return to faithfulness.