Then a demon-possessed man who was blind and unable to speak was brought to Him. He healed him, so that the man could both speak and see. And all the crowds were astounded and said, “Perhaps this is the Son of David!”

When the Pharisees heard this, they said, “The man drives out demons only by Beelzebul, the ruler of the demons.”

Knowing their thoughts, He told them: “Every kingdom divided against itself is headed for destruction, and no city or house divided against itself will stand. If Satan drives out Satan, he is divided against himself. How then will his kingdom stand? And if I drive out demons by Beelzebul, who is it your sons drive them out by? For this reason they will be your judges. If I drive out demons by the Spirit of God, then the kingdom of God has come to you. How can someone enter a strong man’s house and steal his possessions unless he first ties up the strong man? Then he can rob his house. Anyone who is not with Me is against Me, and anyone who does not gather with Me scatters. Because of this, I tell you, people will be forgiven every sin and blasphemy, but the blasphemy against the Spirit will not be forgiven. Whoever speaks a word against the Son of Man, it will be forgiven him. But whoever speaks against the Holy Spirit, it will not be forgiven him, either in this age or in the one to come.
Matthew 12:22-32 (from Holman Christian Standard Bible® Copyright © Holman Bible Publishers.)

What could be more dangerous than doing something so wrong that I couldn’t be forgiven for it?

Jesus was brought a man who could not see or speak. His problems were caused by an unclean spirit that was abusing him. Matthew wrote of him that Jesus healed him. When Pharisees heard people wondering aloud if Jesus might be the “Son of David,” (Messiah), they answered, “The man drives out demons by Beelzebub – the ruler over the demons!” It seems that they could tell that a demon had been driven out of the man, facilitating the obvious healing.

Baal is a generic word that means something like “lord,” “master,” or in some cases, “husband.” Pretty sorry implication in some cases. In Phoenicia, it was used as a proper address for a god or gods, much like the Arabic word, “allah.” In Malaysia or Indonesia, believers rightly call Jesus or Yahweh “Allah.” Baal-Zebul was an insulting name for a god known in Ekron, a Philistine town, as the Lord of the Biting Flies.

Jesus responded to the insults of the Pharisees with information about how wrong it is to speak evil of the Holy Spirit. They could say anything against Jesus and be forgiven, but to speak blasphemy against the Holy Spirit isn’t forgivable. They were misidentifying a work that the Holy Spirit was doing as being done by an unclean spirit.

It is interesting that they chose that spirit to compare. Ahab (husband of the witch, Jezebel,) was succeeded as king by his son, who was named Ahaziah. He lasted for 2 years. Then, he was injured in a fall. He sent some of his servants with the command, “Go inquire of Baal-zebub, the god of Ekron, if I will recover from this injury.”

The Holy Spirit sent Elijah to intercept the messengers with a message for Ahaziah: “‘Is it because there is no God in Israel that you are going to inquire of Baal-zebub, the god of Ekron?’ Therefore, this is what the Lord says: ‘You will not get up from your sickbed—you will certainly die.'” (2 Kings 1: the whole chapter is pretty awesome.)

Without revelation from the Holy Spirit about what He is doing, we are just not able to tell. Perhaps having the gift of discerning of spirits could help us, but even that is a gift of the Holy Spirit. Be very careful before looking at a worker of miracles, or a prophet, or any other supernatural manifestation, and presuming that it is simple and easy to decide what is happening. Even if God is using what we would call an unclean vessel to do a work or bring a word, to speak against Him falsely is exceedingly dangerous.

People speaking against certain styles of music, or dress, or works or words that they do not recognize or understand are frequently blaspheming the Holy One Who sent the worker or speaker. I don’t even want to know what the penalty for making that mistake is.