The author agrees with Paul that sin is not imputed to a believer under grace.
For the Law brings about wrath, but where there is no law, there also is no violation. Rom 4:15 NASB
…but sin is not imputed when there is no law. Rom 5:13 NASB
…for apart from the Law sin is dead. Rom 7:8 NASB
The author also agrees with Paul that we should not sin even though God is not charging it to a believers account: Should we sin because we are no longer under the law but under grace? No.
1 Corinthian’s 10:8 ESV
Nor let us act immorally, as some of them did, and twenty-three thousand fell in one day. 1 Cor 10:8 KJV
We must not indulge in sexual immorality as some of them did, and twenty-three thousand fell in a single day. 1 Cor 10:8 ESV
We should not commit sexual immorality, as some of them did--and in one day twenty-three thousand of them died. 1 Cor 10:8 NIV
This verse is often taken out of context and used to create fear and doubt about a person’s salvation in Jesus or the loss of their salvation if they commit sexual immorality, a misunderstanding of the verse.
In Strong’s, the Greek word used for sexual immorality in this verse is porneuó, and it means:
Original Word: πορνεύω Part of Speech: Verb Transliteration: porneuó Phonetic Spelling: (porn-yoo'-o) Short Definition: I fornicate, practice idolatry Definition: I fornicate; met: I practice idolatry.
1 Cor 10:8 is referring back to Numbers 25, and while the Jews did play the harlot with the daughters of Moab, the big issue is it led to fornication with a false god and idolatry. The Jews bowed down to Baal Peor in worship, the god of the Moabites. First, they yoked themselves to unbelievers, and then those unbelievers led them astray to worship a false God. This was the real adultery, the fortification this verse is talking about that angered God so greatly and aroused His jealousy, the worship of Baal or Peor. This is further verified:
Do not be idolaters, as some of them were. As it is written: "The people sat down to eat and to drink, and got up to revel in idolatry." 1 Cor 10:7 BSB
Therefore, my beloved, flee from idolatry. I speak as to sensible people; judge for yourselves what I say. The cup of blessing that we bless, is it not a participation in the blood of Christ? The bread that we break, is it not a participation in the body of Christ? 1 Cor 10:14-16 ESV
Left alone this unbelief would spread like yeast through Israel’s camp, and God used a plague to stop it and protect those who believed, just like he used the flood to protect the last remaining believers in Noah’s day, a bloodline to bring the Messiah through.
Read it in Numbers 25: While Israel remained at Shittim, the people began to play the harlot with the daughters of Moab. For they invited the people to the sacrifices of their gods, and the people ate and bowed down to their gods. So Israel joined themselves to Baal of Peor, and the LORD was angry against Israel. The LORD said to Moses, “Take all the leaders of the people and execute them in broad daylight before the LORD, so that the fierce anger of the LORD may turn away from Israel.” So Moses said to the judges of Israel, “Each of you slay his men who have joined themselves to Baal of Peor.”
Then behold, one of the sons of Israel came and brought to his relatives a Midianite woman, in the sight of Moses and in the sight of all the congregation of the sons of Israel, while they were weeping at the doorway of the tent of meeting. When Phinehas the son of Eleazar, the son of Aaron the priest, saw it, he arose from the midst of the congregation and took a spear in his hand, and he went after the man of Israel into the tent and pierced both of them through, the man of Israel and the woman, through the body. So the plague on the sons of Israel was checked. Those who died by the plague were 24,000. Num 25:1-9 NASB
Note: Scholars agree that unless 1 Cor 10:8 is talking about a situation that is not written about in the Old Testament, the 23,000 in Corinthians and the 24,000 stated in Numbers are talking about the same situation. They may be general numbers. Maybe 23,516 died, and one writer generalizes it by saying 24,000 and Paul does the same by saying 23,000.
Do you think God would be jealous of a man committing adultery with a woman that had nothing to do with the worship of another God?
Then the LORD spoke to Moses, saying, “Phinehas the son of Eleazar, the son of Aaron the priest, has turned away My wrath from the sons of Israel in that he was jealous with My jealousy among them, so that I did not destroy the sons of Israel in My jealousy. “Therefore say, ‘Behold, I give him My covenant of peace; and it shall be for him and his descendants after him, a covenant of a perpetual priesthood, because he was jealous for his God and made atonement for the sons of Israel.’” Num 25:10-13 NASB
So, should a believer commit sexual immorality/sin since they are not under the law but under grace? No.
We are to walk in the spirit of the letter of the law which is love and sin is not walking in love. But under grace, a believer is not going to lose their salvation, under grace sins are not imputed to their account. You need to be aware though that through the centuries, Satan has used sexual immorality to lead people towards unbelief in the one true God. In his later years, even King David’s son Solomon was led astray by beautiful women to worship false God’s, as were countless others in the Bible. This is why God tells us it is best to not be yoked with unbelievers. This applies to choosing a mate for marriage and any intimate relationship, even things like a partnership in business. If we are yoked to an unbeliever, we need to be aware that if possible, our enemy will use that relationship to lead us astray.
The Jews only got themselves in big trouble with God when they committed adultery with other Gods. Turning away from God to a false god left them with nowhere to sacrifice for their sins and thus subject to the wrath of God. Many More New Covenant Studies: Jesus Did Not Die to See If We Can QualifyA Christians Sins are NOT Counted Against Them,Can a Christian Lose their Salvation by Sinning? NO,
Sins Are NOT Counted Under Grace
Christians Have Diplomatic Immunity
God Forgets Our Sins For His Own SakeWhat is The One Thing That Keeps a Believer in Sin?, How to Stop Sin,
What is the One Unforgivable Sin?Many more HERE.