It is blasphemy against the holy spirit, but what is blasphemy against the holy spirit? If you lie to God are you doomed to hell? Sometimes im not so sure if i did lie to God. Sometimes i say something that i wouldn’t mean with full concentration and then the next “second” i wonder if i lyed to God and commited and unforgivable sin. But i don’t recall to have said a lie to God, hence that would be stupid. But sometimes i wonder if i ever said a lie subconsciously to God. So what is the unforgivable sin?
Dying in the state of unrepentance.
God willingly forgives any sin, no matter how great, but only if we seek it by repenting. God won’t forgive our sins forcefully, we must seek Him. Therefore by not repenting, we are saying, “God is wrong, I am right”, which is blasphemy. And since it is through the Holy Spirit that we receive the grace of sanctifying grace, paid for by the work of Christ on the cross, that we say unrepentance is blasphemy against the Holy Spirit by denying the grace He offers.
[quote="Timi Celcer]So what is the unforgivable sin?
Yes I agree with this. I was taught that the sin against the Holy Spirit (the “unforgivable sin”) means more a state of mind than a particular word spoken. No sin is unforgivable as long as we are alive, but, as bzkoss said, we must freely choose to repent and seek God’s forgiveness. And if we become hardened and obstinate in our own thinking and refuse God’s mercy to the bitter end, then WE make it impossible to be forgiven, because we are not seeking forgiveness. So the moral of the story is stay close to God, confess often and sincerely, and do our best always to be faithful to Him.
I look at two things with this statement of the Lord…
Why and when did he tell that to us?
Jesus heals an oppressed man from a demon. The Pharisees accused, not Jesus, but His Spirit and intentions of evil. That’s pitting ourselves against the very nature of God, which is to deliver men from sin and hell.
The end of the teaching alludes to sins forgiven out of ignorance, which is just not realizing who Jesus was, for example. At the His cross, He said, “forgive them, for they know not what they do.” The pharisees were examining His Spirit and still pitting themselves against Him.
Also, the words of John the Baptist come to mind. Woe to those who call good-evil and evil-good.
The Catechism explains it prettly succinctly:
CCC 1864 “Therefore I tell you, every sin and blasphemy will be forgiven men, but the blasphemy against the Spirit will not be forgiven.”  There are no limits to the mercy of God, but anyone who deliberately refuses to accept his mercy by repenting, rejects the forgiveness of his sins and the salvation offered by the Holy Spirit.  Such hardness of heart can lead to final impenitence and eternal loss.
 Mt 12:31; cf. Mk 3:29; Lk 12:10.
 Cf. John Paul II, DeV 46.
God doesn’t force Himself on anyone. If you don’t repent and accept His mercy, you can’t be forgiven. If you don’t take the lid off the cup, God can’t fill it up.
Voting for Obama.
All these answers have addressed the heart of the matter better than mine. The unrepented state of man.
The Catechism passage also cites John Paul II’s encyclical Dominum et Vivicantem. Paragraphs 46-48 expand upon this question in even greater depth. I would recommend reading through that as well.