Blasphemy is an offense to a deity. It is an insult or irreverence towards a religion or towards what is considered sacred. It is the defamation of the name of God.
In my life, I have heard lots of people blaspheme against the Holy Spirit, say that God does not exist, or that God is unjust, that God does not listen to them. In the midst of anger we say quantities of things, sometimes without measuring the consequences; blasphemy is an unforgivable sin, we can not question the things that God does, he only knows why things happen to us, many times he allows things to happen so that we have an apprenticeship and we humans do not see it from that way.
Luke 12:10
And everyone who says a word against the son of man will be forgiven, but whoever blasphemes against the holy spirit will not be forgiven.
I always thank God for everything that happens in my life, because many of those things, although they have hurt me a lot, have always left me with an apprenticeship, on occasion I have seen that God wanted to show me something many times and in different ways and by many means and I went ahead doing what seemed to me, and everything went wrong, because I understood that it is not what I want is what God decides.
A couple of years ago I went to the wake of the son of a close relative to the family, it was very painful because he was a boy and he was only 6 years old. He was his only son and he died in a terrible way because a wall fell on him, the mother in the midst of her pain she cried out that God did not exist and if she existed it was unjust because she took her son away. After a few months of that tragic event, God showed her a dream where she saw that her son was a man and had become a delinquent and died in a confrontation, because that day he asked God for forgiveness because God had removed all that suffering from having seen his son sunk in perdition and decided to take him turned into an angel. That event was kept in my mind and every time I remember it I see the greatness of God