Then was brought unto him one possessed with a devil, blind, and dumb: and he healed him, insomuch that the blind and dumb both spake and saw. And all the people were amazed, and said, Is not this the son of David? But when the Pharisees heard [it], they said, This [fellow] doth not cast out devils, but by Beelzebub the prince of the devils."
The Pharisees, with minds so blinded by hate, made the absurd claim that Jesus overpowered demons with the help of the leader of the demons. To this, Jesus told them:
"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. 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. (Matthew 12:31-32)
I've heard of those who feared that they were condemned because they might have said an idle word against the Holy Spirit. But such fears are unjustified. Context is always key to right interpretation, and the context speaks of something far more sinister than an idle word.
The Pharisees with only a few exceptions were bitterly opposed to Jesus and would accept no evidence of His divinity. After He had performed many signs and wonders, the Pharisees demanded that He perform a sign. (Matthew 12:38) Jesus told them they would receive no sign but the sign of Jonah. He also said that the men of Ninevah would rise up in judgement against them. (Matthew 12:39-42)
To speak a word against Jesus, to resist Him, to argue with Him, to reject Him for awhile, to even curse Him as Peter did (Matthew 26:74); these were all forgivable. God's grace is inexhaustable. But what about those who completely and totally reject God's grace? It is such as these who commit the unpardonable sin.
In John 5:36, Jesus said that the Father's testimony of His mission and purpose was to be found in the works which the Father had given Him to do. One of these works was casting out demons. When the Pharisees not only rejected Jesus, but the power of the Father through the Holy Spirit, they sealed their own fate. God could not forgive them if they so hardened their minds and hearts against God so as to call God satan. How could they repent and be saved if they could no longer tell the difference between good and evil, God and satan? They most likely had reached the point of total depravity and had filled their minds with total darkness. If so, they could no longer be reached, and were lost forever.
There is a point of no return. If today, the Spirit of God is speaking to you to accept Jesus Christ as your Lord and Savior, do not resist the call. There may come a time when it is too late. If you die without having turned to Christ, or if you completely harden your heart to Him in this life, there will be no second chances.