Unbelief is not the unforgivable sin; no one can choose what to believe anyway, and of the 244 mentions of “pistis” in scripture, none of them are about “making a decision” about the epistemic truth of god-talk. In all instances, “belief”, “faith”, the words used for “pistis” are about God’s “divine persuation” to His will, which is goodness; that draw being entirely the meaning of faith and belief. Our only choice is to participate or not. That’s it. Non participation is the unforgivable sin; not whether we think there is or is not some “Big Other” keen on sending folks to Hell because His existence wasn’t at all clear to many, and God not making it crystalline Himself.
“According to such an exegesis, ‘blasphemy’ does not properly consist in offending against the Holy Spirit in words; it consists rather in the refusal to accept the salvation which God offers to man through the Holy Spirit, working through the power of the Cross … If Jesus says that blasphemy against the Holy Spirit cannot be forgiven either in this life or in the next, it is because this ‘non-forgiveness’ is linked, as to its cause, to ‘non-repentance,’ in other words to the radical refusal to be converted. This means the refusal to come to the sources of Redemption, which nevertheless remain ‘always’ open in the economy of salvation in which the mission of the Holy Spirit is accomplished.”
Pope John Paul II, Dominum Et Vivificantem.
That is to say, it is unforgivable to be numb to your actions, unremorseful because the Holy Spirit cannot work in you.
To grieve the Holy Spirit is to also say that unbelievers are unforgivable merely for the fact they don’t believe in God; for it is to deny the Holy Spirit is at work in them as well, especially when their lives are very much bearing its fruit.
“… I found some astonishing things in the course of my study that had never occurred to me. Frankly, in the days when I thought I’d had it with religion, I just found the whole thing absolutely incredible. These doctrines seemed unproven, abstract. And to my astonishment, when I began seriously studying other traditions, I began to realize that belief — which we make such a fuss about today — is only a very recent religious enthusiasm that surfaced only in the West, in about the 17th century. The word “belief” itself originally meant to love, to prize, to hold dear. In the 17th century, it narrowed its focus, for reasons that I’m exploring in a book I’m writing at the moment, to include — to mean an intellectual assent to a set of propositions, a credo. “I believe:” it did not mean, “I accept certain creedal articles of faith.” It meant: “I commit myself. I engage myself.” Indeed, some of the world traditions think very little of religious orthodoxy. In the Quran, religious opinion — religious orthodoxy — is dismissed as “zanna:” self-indulgent guesswork about matters that nobody can be certain of one way or the other, but which makes people quarrelsome and stupidly sectarian.
“So if religion is not about believing things, what is it about? What I’ve found, across the board, is that religion is about behaving differently. Instead of deciding whether or not you believe in God, first you do something. You behave in a committed way, and then you begin to understand the truths of religion. And religious doctrines are meant to be summons to action; you only understand them when you put them into practice.”
Karen Armstrong, My Wish: The Charter For Compassion, Ted Transcript March 2008