I am going to share a portion from Dr. John R. Rice’s book entitled The King of the Jews, which is a commentary on Matthew.  His study of the unpardonable sin reaches the following conclusions:

“The following facts are evidently true about the unpardonable sin:  (1) There is only one unpardonable sin (Matthew 12:31); it is not murder nor adultery nor cursing, and not simply the rejection of Christ;  (2) Saved people cannot commit the unpardonable sin since all their sins are already pardoned and they cannot come into condemnation (John 5:24, Colossians 2:13).  To the saved person salvation is a finished, present possession.  They are kept by the power of God through faith unto salvation (John 10:28,29, I Peter 1:5).  This sin is committed only by lost people;  (3) The unpardonable sin is committed only by sinners of great enlightenment such as these Pharisees here who the prophecies and saw marvelous evidence of the power of Christ.  (See the enlightenment pictured in Hebrews 6:4,5).  In the Bible, Pharaoh, at the time of Moses, and Judas Iscariot seemed to have committed the unpardonable sin, as the Antichrist will evidently do;  (4) The unpardonable sin is connected always with the rejection of Christ by a sinner; not all who reject Christ as Saviour commit the unpardonable sin but each one may do so;  (5) The unpardonable sin is a complete and final rejection of Christ so definite and blasphemous that it insults and drives away the Holy Spirit forever.  Then He no longer moves the heart, brings conviction or arouses the desire for salvation.  Usually those who feel they have committed the unpardonable sin have not.  One who has is unconcerned, since the Holy Spirit has withdrawn from him;  (6) The desire to be saved proves that one has not committed the unpardonable sin (Revelation 21:6 and 22:17).”