What is the Unpardonable Sin?

Then a demon-oppressed man who was blind and mute was brought to him, and he healed him, so that the man spoke and saw. And all the people were amazed, and said, "Can this be the Son of David?" But when the Pharisees heard it, they said, "It is only by Beelzebul, the prince of demons, that this man casts out demons." Knowing their thoughts, he said to them, "Every kingdom divided against itself is laid waste, and no city or house divided against itself will stand. And if Satan casts out Satan, he is divided against himself. How then will his kingdom stand? And if I cast out demons by Beelzebul, by whom do your sons cast them out? Therefore they will be your judges. But if it is by the Spirit of God that I cast out demons, then the kingdom of God has come upon you. Or how can someone enter a strong man's house and plunder his goods, unless he first binds the strong man? Then indeed he may plunder his house. Whoever is not with me is against me, and whoever does not gather with me scatters. Therefore I tell you, every sin and blasphemy will be forgiven people, but the blasphemy against the Spirit will not be forgiven. And whoever speaks a word against the Son of Man will be forgiven, but whoever speaks against the Holy Spirit will not be forgiven, either in this age or in the age to come.

(Mat 12:22-32)

I have seen many discussions on that particular theological dilemma. What is this sin that Jesus is talking about so strongly, and can a Christian rest peaceful, or must we fear this horror? I guess there are two camps on this, one of them being the Arminian camp, believing in losing of salvation, and hence viewing this sin as reality possible and existing if they fault at will.
I do not opt for that camp. If what Paul says in Romans:

And he who searches hearts knows what is the mind of the Spirit, because the Spirit intercedes for the saints according to the will of God. And we know that for those who love God all things work together for good, for those who are called according to his purpose. For those whom he foreknew he also predestined to be conformed to the image of his Son, in order that he might be the firstborn among many brothers. And those whom he predestined he also called, and those whom he called he also justified, and those whom he justified he also glorified. What then shall we say to these things? If God is for us, who can be against us?
(Rom 8:27-31)

is true, there is no way that a God's Elect can commit this sin. So let me share with you what Dr. Charles Stanley has to say on the subject:

No one today can commit the unpardonable sin. According to the Bible, the only action God will not pardon is blasphemy against the Holy Spirit, committed by the Pharisees. The Jewish religious leaders were shown compelling evidence that Jesus was God’s Son. But they chose to undermine Him in hopes of maintaining their own power. After witnessing Christ’s miracles, the Pharisees blasphemed by claiming His supernatural power was from Satan. In Matthew 12:22-32, Jesus responds to their sin by warning that whoever spoke this way against the Holy Spirit wouldn’t be forgiven.

People today don’t have the undeniable physical presence of Jesus Christ in the world. So they can’t recreate the Pharisees’ sinful event. But it’s still possible to end up in an unpardonable state. This happens when a person rejects the Holy Spirit’s call to salvation and holy living, and then dies in a condition of unbelief.

The stages leading to an unpardonable state are simple. An unbeliever chooses to sin, even though he knows it’s wrong. He resists the Holy Spirit’s gentle prompts toward conviction and salvation. Over many years, this hardens his heart against God. A time comes when the Holy Spirit makes no impression. Any desire for the Lord has dried up. No sermon or song can move him. His heart is hardened to the Gospel.

No sin can separate you from God’s love. Only a conscious decision to reject the Lord can result in your spending an eternity apart from Him. Don’t wait another minute to receive His offer of salvation.

by Dr. Charles Stanley