The blasphemy of the Holy Spirit

“But when the Pharisees heard this, they said, ‘It is only by Beelzebub, the prince of demons, that this fellow drives out demons.’” Matthew 12:24
Many Christians worry about committing the ‘unpardonable sin’, that is, the blasphemy of the Holy Spirit. Is it possible for a believer to do this? To answer this question we need to understand what the blasphemy of the Spirit is, because Jesus tells us this is the only sin that will not be forgiven (Matt. 12:31-32).
The blasphemy of the Spirit is exactly what the Pharisees here are guilty of. They see Jesus casting out a demon that caused the afflicted man to become deaf and mute. The casting out of a demon like this was considered by the Jews to be something only Messiah could do, because the Jewish method of exorcism was to first ask the demon what his name was. A man made mute by a demon could not answer, and the demon could not be driven out.
However, when Jesus cast the mute demon out – a sign that He was indeed the Messiah – the Pharisees attributed that work of the Holy Spirit to Satan. Thus, they blasphemed against the Holy Spirit, and in so doing, reject the only means by which they could receive salvation. This is why the blasphemy of the Spirit is the unpardonable sin – because one must respond to the Holy Spirit favourably to receive mercy, forgiveness, and salvation.