Mark 3:22; The scribes who came down from Jerusalem were saying, "He is possessed by Beelzebul," and "He casts out the demons by the ruler of the demons."
Mark 3:23; And He called them to Himself and began speaking to them in parables, "How can Satan cast out Satan?
Mark 3:24; "If a kingdom is divided against itself, that kingdom cannot stand.
Mark 3:25; "If a house is divided against itself, that house will not be able to stand.
Mark 3:26; "If Satan has risen up against himself and is divided, he cannot stand, but he is finished!
Mark 3:27; "But no one can enter the strong man's house and plunder his property unless he first binds the strong man, and then he will plunder his house.
Mark 3:28; "Truly I say to you, all sins shall be forgiven the sons of men, and whatever blasphemies they utter;
Mark 3:29; but whoever blasphemes against the Holy Spirit never has forgiveness, but is guilty of an eternal sin"--
Mark 3:30; because they were saying, "He has an unclean spirit."
Blasphemy is saying that something from God is from the devil, and something from the devil is from God.
In the passages above, the scribes were saying Jesus was casting out demons with an evil spirit. (from Beelzebul).
There are some Christians today who say God is control of everything, he is even in control of me when I sin (so ultimately God is causing me to sin).
This is the same as blasphemy of the Holy Spirit. saying that evil (sinful) things are caused by God (Holy Spirit).