>>718933578
It seems arbitrary because you don't understand what God is in the Christian sense. I don't blame you, most Christians don't understand it either.
God, and specifically the Holy Spirit as an aspect of God, is love and mercy and compassion. "Blasphemy against the Holy Spirit" is not about insulting a figure of reverence or authority, the same passages that name this an unforgivable sin say that even slandering Jesus Christ Himself can be forgiven. What is unforgivable is to deny the idea of love and forgiveness itself, to refuse to change for the better when given the opportunity to do so. The only way to keep yourself out of Heaven is to willingly condemn yourself to Hell.