ANSWER: First, let us take a look at the primary verses in the Bible that discusses this subject, "every sin and blasphemy shall be forgiven to men except the blasphemy against the Holy Spirit . . . but whoever speaks against the Holy Spirit, it shall not . . . " (Matthew 12:31 - 32).
The English word blasphemy is translated in the Bible from the Greek word blasphemia (Strong's Concordance #G988). It means to vilify, speak evil of, or rail against a person. Webster's Dictionary defines the word as meaning to insult, show contempt of or not revere God sufficiently. The word can be applied to a person who claims some or all of God's attributes. The word profane, a synonym, is defined as abusing or treating with contempt or disdains that which is sacred.
The above shows that blasphemy is not done by accident. It is done when one has the knowledge of the person, object, or idea that is being discussed. This was the initial charge against Jesus that condemned him to die (Matthew 26:63 - 66).
The Bible makes a distinction between what it means to commit this act against the Son of Man (Jesus) versus the Holy Spirit. This, however, begs the question as to why there is a distinction. Why are sins against Jesus forgiven but not those against the Holy Spirit? Does this mean that God's Holy Spirit, given upon repentance and baptism, is somehow GREATER than the Savior of mankind who made the gift possible?
People, out of their lack of full knowledge and understanding, may wrongly commit blasphemy against Jesus and still receive forgiveness. For example, many people living at the time of Jesus - who saw his miracles and heard him speak - concluded that he was from God. However, they also blasphemed because they denied and rejected He was God's son and the Messiah. Yet, because of their ignorance, this sin (upon repentance) will be forgiven.
". . . so that they would not see with their eyes and understand with their hearts, and be converted, and I would heal them" (John 12:40, HBFV)
Speaking against or committing blasphemy against God's Holy Spirit is a different matter entirely. Although God certainly worked with a few people in the Old Testament, he did not make His Spirit available to mankind in general until Pentecost in 30 A.D. (Acts 2:16 - 21).
To receive of the gift of God's Spirit, a person must accept and believe that Jesus is God's son and the Savior of the world, repent of sin, be willing to surrender their entire life to the will of God, and go under the waters of baptism (Acts 2:38). If, after all this and receiving the spirit a person with full knowledge REJECTS God and commits blasphemy (has contempt for the spirit within them), her or she then becomes one of God's adversaries (like the devil). Someone who does this has no hope of forgiveness, as they now refuse to repent of their sins and change. The apostle Paul explains this further.
26 For there is no longer any sacrifice that will take away sins if we purposely go on sinning after the truth has been made known to us (Hebrews 10:26)
The God of the Bible is one of mercy, forgiveness, and love. However, if a person willfully chooses to commit blasphemy against him, he will honor their choice. He will ultimately put them out of their misery in the lake of fire (Revelation 20:14 - 15).