Some argue that the Bible is contradictory concerning blasphemy of the Holy Spirit, since Matthew and Mark say that blasphemy against the Holy Spirit will not be forgiven, but Scripture elsewhere says that any sin can be forgiven. What exactly is blasphemy of the Holy Spirit, and does Matthew and Mark contradict what Scripture teaches in other places?
31 Therefore I tell you, every sin and blasphemy will be forgiven people, but the blasphemy against the Spirit will not be forgiven. 32 And whoever speaks a word against the Son of Man will be forgiven, but whoever speaks against the Holy Spirit will not be forgiven, either in this age or in the age to come. Matthew 12:31-32
but whoever blasphemes against the Holy Spirit never has forgiveness, but is guilty of an eternal sin”— Mark 3:29
Blasphemy of the Holy Spirit probably ultimately refers to unbelief. The Bible clearly teaches that it is through faith, not works, that a person is saved. This means that no matter what a person does, if that person ends up having genuine faith in Jesus, that person will be forgiven and saved.
What exactly does it mean to speak against the Son of Man, or to speak against the Holy Spirit? It cannot simply mean to say words against the Son of Man or the Holy Spirit because we know that many people who have spoken words against Jesus and the Holy Spirit ended up having faith and being saved.
“Speaking against” the Son of Man or the Holy Spirit probably refers to a hardness of heart that refuses to acknowledge them as who they really are: God. This kind of hardness of heart results in unbelief, and if a person continues in unbelief, that person will not be forgiven.
To read more answers to alleged and apparent contradictions in the Bible, see “Contradictions” in the Bible Answered.
These books are also excellent resources: