In Mark 3, those who try to turn the work of God into the work of the devil show by so doing that they are so far gone, so deeply enmeshed in a spiritually inverted reality, that there is no reaching them. Some of you will recall the dwarves as depicted by C.S. Lewis in the last book of the Narnia series. The dwarves had been brought by Aslan the Lion into the glories of the New Narnia, which stood for heaven or the kingdom of God. These stubborn dwarves sat smack in the middle of a sunlit meadow full of wildflowers and were being fed fruit and vegetables more exquisitely flavorful and fresh than anyone had ever before imagined was possible.
Yet their minds were darkened, their hearts were cold. And so they were convinced they were sitting in the middle of a stinky old stable being fed moldy bread and cow manure. When one of the other characters asks Aslan what can be done for these hapless figures, the answer comes back that nothing can be done. When black becomes white and white becomes black, when evil is good and good is evil, people are gone. God can't get through to them. The reason the unpardonable sin can never be forgiven is because it will never, ever be recognized as a sin. Even if God came to such people bearing the sweet fragrance of his grace, all these people would smell would be the stink of a rotting corpse. They won't be forgiven because they cannot be forgiven and they cannot be forgiven because they have come to believe that the gospel's elixir of life is strychnine: pure poison.