Personally, this has always mystified me. How can anything possibly ever be done that is so bad as to be unforgivable in the eyes of the God of the Bible, when he forgave King Ahab for his unbelievable atrocities. The man was a fiend, yet God chose to restore him to power.
Nothing about the 'sinning against the Holy Spirit as the unforgivable sin' makes any sense in light of the story of King Ahab.
Jean