Referring to Matthew 12:31 Jesus says, "And so I tell you, every sin and blasphemy will be forgiven men, but the blasphemy against the Spirit will not be forgiven." Consider the background of this verse. In chapter 11 certain Jewish cities rejected Jesus. Also, John the Baptist raised serious doubts about Jesus because his expectations were not fulfilled. Matthew 12:31,32 refers to the most serious rejection of Jesus-the rejection of the Pharisees.
One of the rejection episodes is in the Beelzebub story (Matthew 12:22-37). It begins when Jesus heals a blind mute. The frightening thing for the Jewish leaders is that the people are so enthused by the miracle that they begin to wonder out loud if Jesus might not be "the Son of David"-that is, the Messiah (vs. 23).
The frustrated Pharisees cannot deny the reality of the miracle, but they can deny that it came from God. Their solution is that Jesus is in league with the "prince of demons" (vs. 24).
Jesus immediately takes the offensive by telling them that if He were curing people through the power of demons, then Satan's kingdom would be divided against itself and would be in ruins (vss. 25-28). Jesus argues that actually, he is the devil's greatest enemy. He likens Himself to a thief who ties a strong man up so he can raid his house (vs. 29). In other words, Jesus the Christ (God with us) has invaded the territory of "the prince of this world" (John 12:31; 14:30; 16:11) to rescue God's children.
The climax of the confrontation in the Beelzebub story comes in Matthew 12:30-32. In this passage Jesus not only warns His hearers that there is no neutrality in the great struggle between good and evil, but He goes on to say that anyone who credits the work of God to the devil has committed the unpardonable sin (vs. 31). While it is technically true that people can speak against the Son and still be forgiven, they cannot do so and be forgiven if they are under the conviction of the Holy Spirit that Jesus is the Messiah. To do so would be to reject the prompting of the Holy Spirit in their heart and mind. The result is a hardened conscience (1 Timothy 4:2); Titus 1:15) that can no longer respond to the Spirit's work of leading people to repent of and confess their sin (John 16:8). Such rejecters are beyond the reach of God's Spirit, for they have tuned out the only channel through which God can reach them. When that is done, they are beyond hope. They have committed the unforgivable sin.
Many sensitive Christians worry that they have committed the unpardonable sin. The very fact that they are concerned is an indication that they are still listening for the Spirit and desire to respond to Him. Frederick Bruner is right on target when he writes, "the spirit of the sin against the Spirit is an unworried adamancy. It is impenitence, the unwillingness to repent… It is not careless acts, it is a hardened state" (Bruner, 1:462).
Jesus goes on to claim that the true state of people can be told by the words that come out of their mouths (Matthew 12:33-37). Such a truth does not bode well for the Pharisees, whose mouths have recently set forth the view that Jesus' actions were inspired by the devil rather than God. If they continue in that line, Matthew 12:22-37 implies, they will eventually commit the unpardonable sin.