God's law explicitly states that "If a man also lie with mankind, as he lieth with a woman, both of them have committed an abomination: they shall surely be put to death; their blood shall be upon them." (Leviticus 20:13).
This isn't man's law today except in a few places. Men excuse this serious sin which requires the death penalty. And this OT sin didn't simply disappear with the new covenant. Paul writes:
28 And even as they did not like to retain God in their knowledge, God gave them over to a reprobate mind, to do those things which are not convenient; 29 Being filled with all unrighteousness, fornication, wickedness, covetousness, maliciousness; full of envy, murder, debate, deceit, malignity; whisperers, 30 Backbiters, haters of God, despiteful, proud, boasters, inventors of evil things, disobedient to parents, 31 Without understanding, covenantbreakers, without natural affection, implacable, unmerciful: 32 Who knowing the judgment of God, that they which commit such things are worthy of death, not only do the same, but have pleasure in them that do them. (Romans 1:29-32)
Roman and Greek culture celebrated sexual deviancy and didn't condemn it as the captical crime it is. We have returned to those pagan values. If you read the attributes which characterize men then, you will see our own venal tendencies.
These reprobates deserve death then and they knew it (ἄξιοι θανάτου εἰσίν -- present tense). It's still a sin deserving of death and they know it. That is why they are so vindictive in their attacks against those who hold up God's standards of righteousness. Those who hold to "traditional marriage" are branded haters or worse. Evil is called good. Good is called evil.
20 Woe unto them that call evil good, and good evil; that put darkness for light, and light for darkness; that put bitter for sweet, and sweet for bitter! 21 Woe unto them that are wise in their own eyes, and prudent in their own sight! 22 Woe unto them that are mighty to drink wine, and men of strength to mingle strong drink: 23 Which justify the wicked for reward, and take away the righteousness of the righteous from him! 24 Therefore as the fire devoureth the stubble, and the flame consumeth the chaff, so their root shall be as rottenness, and their blossom shall go up as dust: because they have cast away the law of the LORD of hosts, and despised the word of the Holy One of Israel.
You may encounter this verse again at the end of the world.
12 And I saw the dead, small and great, stand before God; and the books were opened: and another book was opened, which is the book of life: and the dead were judged out of those things which were written in the books, according to their works. (Revelation 20:12)
But I hope not. Today is the day of salvation, where you no longer trust in your own works to save, but accept God's pardon. (2 Corinthians 6:2)
God also said He would give us a New Covenant where He would "forgive their wickedness and recognize their sins no more"..
Jesus died for all our sins, past/present/future if we only confess to Him and accept Him as our Savior.
Without His sacrifice, we would all be as doomed as those who broke his laws in the Old Covenant for much "lesser" violations.
What does the New Covenant say is the only unforgivable sin? Is the New Covenant any less believable/valid than the Old Covenant?