What is the sin that cannot be forgiven? To believe that the Holy Spirit CANNOT -- cannot be the power behind God's presence here and now, cannot be a companion in creative power of the Father, cannot be the cause of the incarnation of the Son in Mary'sy womb, cannot make the sacraments effective and meaningful, cannot transform the cross into grace, cannot bring about healing, cannot bring about conversion and new life, cannot bring about forgiveness. If one does not beleive in the power of the Holy Spirit to forgive sins, how can one's sins be forgiven. This is not a question of God's boundless mercy. Rather, a question of the disposition of one's heart, the disposition of beleif or non-belief.
God's mercy accepts anyone in forgiveness, but without belief in that mercy how can one even begin to turn to Him.
