I was taught that the unforgivable sin entailed knowing completely the role and goal of the Holy Spirit and then fighting against that. So one had to be very righteous to get to that place and then would need to turn, not unlike Lucifer is depicted as doing in the Bible traditions.

Today I believe the concept that Jesus teaches in A Course In Miracles where he says that we are all mistaken and that there is no sin.

Primarily because if sin were possible then God could not be God.

This is why true forgiveness of the original error of belief that the Son could be separate from God and all of its subsequent consequences is how we free humanity from the bondage of death and torture and put all of creation on a level playing field where we can have the opportunity to make decisions that will allow us to live in harmony.

This is possible because God IS and is all that is or ever will be worlds without end.