(This sin has nothing to do with unbelief, Jesus himself, God the Father, or personal sins of the flesh).
Mat 12:24 But when the Pharisees heard it, they said, This fellow doth not cast out devils, but by Beelzebub the prince of the devils.
Mat 12:28 But if I cast out devils by the Spirit of God, then the kingdom of God is come unto you.
Mar 3:29 But he that shall blaspheme against the Holy Ghost hath never forgiveness, but is in danger of eternal damnation:
Mar 3:30 Because they said, He hath an unclean spirit.
Mat 12:31 Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy against the Holy Ghost shall not be forgiven unto men.
Mat 12:32 And whosoever speaketh a word against the Son of man, it shall be forgiven him: but whosoever speaketh against the Holy Ghost, it shall not be forgiven him, neither in this world, neither in the world to come.
The Pharisees blasphemed against the Spirit for they said Jesus had an unclean Spirit, and attributed the works He did to the devil, which they said they were evil works, which Jesus did good works, and Jesus pointed out that if He is casting out devils then He is of the kingdom of God.
A person can blaspheme against the Son, the flesh, and be forgiven, but cannot blaspheme against the Spirit.
Which Saul went against the Church but did not blaspheme against the Spirit, for he was a Pharisee, and zealous of the traditions of his fathers, which he only went against the Son, the flesh, and not against the Spirit, then Jesus met him and then He followed Jesus, and became Paul.
Blaspheme against the Spirit is attributing evil to God when He is good.
Which some people say God does not love me, He is punishing me, He is responsible for natural disasters, which is not true for we are under grace.
The Bible testifies that there is a God that created all things, and of His attributes, which one of them is love, for He provided food, and the means to make clothing, and shelter, so the world is without excuse, and testifies of the 2 greatest laws, love God, and love people.
Since creation testifies that God loves people, and is good, then people should not believe that God is evil, but good.
And further proof coming from the Bible that God is love, and good.