I remember an Irish commedian, David Allen. He had a show that PBS broadcast called "David Allen at Large" where he would do a combination of sit down commedy and skits.
One skit I remember was a man walking into a church with two confessionals. The first was labeled "Forgivable Sins" and the second was labled "Unforgivable Sins." As the man approaches the "Forgivable Sins" confessional, he stops and thinks and then heads for the "Unforgivable Sins" confessional.
He steps in and then falls. Flames reach up through the confessional and you hear a satanic laugh as he catches another soul.
In my years of prison work, I often get asked what is the unforgivable sin or what is the "Blashpemy against the Holy Spirit" that Jesus talks about. The men who ask this question are very serious because sin and forgiveness are not "nice things" to them, but are life and death. Too many of them think that what they have done or who they are is beyond redemption. They are certain that they have committed unforgivable sins.
To the best of my research and prayer and experience, the "unforgivable sin" and "blasphemy against the Holy Spirit" is to say that God cannot forgive this sin. The only sin that God cannot forgive is the one that you won't let Him.
In reality, saying that God can't forgive this sin is a type of pride. It is saying to God that the death of His Son, Jesus Christ, was not enough to pay for this sin. To which I answer "what more could God do to forgive your sin?"
As sinful creatures, we need to realize that God wants to forgive our sins and waits for us to begin to say "Father, I have sinned against heaven and before you." God waits for us to lay our sins at the foot of the cross so they can be (and will be) forgiven.