The only sin being mentioned by Jesus Christ about being unforgiveable was “blasphemy of the Holy Spirit”, sometimes called the Holy Ghost – https://www.biblegateway.com/passage/?search=Matthew+12%3A31-32&version=KJV and https://www.biblegateway.com/passage/?search=Mark+3%3A29&version=KJV; see below for the Bible verses in the links. These verses make it clear that blasphemy of the Holy Spirit, or Holy Ghost, is not forgivable. This was Jesus speaking and He knew the minds and thoughts of the Pharisees who were mentioned just before He made the comments.
Matthew 12:31-32 King James Version
31 Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy against the Holy Ghost shall not be forgiven unto men.
32 And whosoever speaketh a word against the Son of man, it shall be forgiven him: but whosoever speaketh against the Holy Ghost, it shall not be forgiven him, neither in this world, neither in the world to come.
Mark 3:29 King James Version
29 But he that shall blaspheme against the Holy Ghost hath never forgiveness, but is in danger of eternal damnation.
If you die having never accepting Jesus Christ in your heart, you will find Hell is a real place. I know some false Christian denominations remove Hell references from their Bibles and other false Christian denominations never preach about Hell. When you consider how many times Jesus Christ talked about Hell, that should be a clear indicator that Jesus knew Hell was a real place. Unfortunately, too many people think they are Christians, but have never done what the Bible said you have to do to become a Christian.
When I was growing up there were false Christian denominations out there, but lately the number has increased substantially. If that’s not bad enough, many of the true Christian denominations’ pastors have stopped preaching about Hell as their congregations don’t want to hear about it.
Other Forgiveness Sundays posts: https://upsdownsfamilyhistory.wordpress.com