Matthew 12:31-32 Therefore I say to you, every sin and blasphemy will be forgiven men, but the blasphemy against the Spirit will not be forgiven men. Anyone who speaks a word against the Son of Man, it will be forgiven him; but whoever speaks against the Holy Spirit, it will not be forgiven him, either in this age or in the age to come.
The above passage of scripture, in which Jesus defines an unpardonable sin has baffled Bible readers for centuries. The idea of an act, which according to conventional reasoning, would irrevocably doom one to eternal torment, is fearsome indeed. The fact that there seems to be no real consensus on what that act might be makes the entire concept even more troubling.
As I read the broader context in which Jesus defines this sin, I notice that his remarks follow the account in which the Jewish religious leaders attribute Jesus' power to the Devil as opposed to it being from God. That observation leads me to conclude that what Jesus was noting in this event was the misrepresentation of God's power and operation. Therefore, in Jesus' words, the ultimate sin or mistake is to entertain and promote a false picture of God. In doing so we promote unloving behaviors which are destructive in all ages. I believe that forgiveness, here, does not speak of God's acceptance but of humankind's escape from the consequences of that sin, not as judicial decree but a natural fact of life. Sin is the opposite of love as far as behavior is concerned.
"Unlovingness" is perpetually sinful/harmful but not in the OT sense of violating a written law. The violation is of the law of the heart.
I'll conclude with a final thought. Even if one insists that this forgiveness must involve God's acceptance and approval, I refer to Hebrews 8:12, which says that God does not remember our sins any more. If sin is no longer remembered, forgiveness of sin by God becomes impossible, but at the same time unnecessary.