Jesus followed up His refutation with a solemn warning. The words "truly I say to you" or "I tell you the truth" occur13times in this Gospel, always on Jesus" lips. This phrase occurs30 times in Matthew , six times in Luke , and25 times in John where the "truly" is always double. It denotes that Jesus was speaking out of His own authority. A comparable expression in the Old Testament Isaiah , "As I live, says the Lord."[source]
"His use of "Amen" to introduce and endorse his own words is without analogy in the whole of Jewish literature and in the remainder of the NT. ... "Amen" denotes that his words are reliable and true because he is totally committed to do and speak the will of God. As such, the Amen-formulation is not only a highly significant characteristic of Jesus" speech, but a Christological affirmation: Jesus is the true witness of God." [1][source]
"In light of the context this [2] refers to an attitude (not an isolated act or utterance) of defiant hostility toward God that rejects His saving power toward Prayer of Manasseh , expressed in the spirit-empowered person and work of Jesus. It is one"s preference for darkness even though he has been exposed to light (cf. John 3:19). Such a persistent attitude of willful unbelief can harden into a condition in which repentance and forgiveness, both mediated by God"s Spirit, become impossible. This person is guilty (enochos, "liable to, in the grasp") of an eternal sin (sing, the ultimate sin because it remains forever unforgiven; cf. Matthew 12:32). Judas Iscariot (cf. Mark 3:29; Mark 14:43-46) proved the reality of these words." [3][source]
We should not focus so exclusively on the exception to forgiveness that we fail to appreciate the breadth of forgiveness that Jesus offered here. "All sins" means all classes and types of sins, not all sins without exception. Jesus was not teaching universalism, the theory that everyone will go to heaven. Blasphemy is a type of sin, namely, speech that is hostile, malicious, injurious, and derogatory of God. This was the type of sin the scribes were committing. [source][source][source]
The scribes came perilously close to committing an unpardonable sin because they attributed the power of Jesus" exorcisms to Satan rather than to the Holy Spirit (cf. Mark 1:11-12). [source][source][source]
"Having rejected the testimony of the Father, the Song of Solomon , and now the Spirit"s miraculous authentication, nothing more could be done for the salvation of those religious leaders." [4][source]
"Those who most particularly should heed the warning of this verse today are the theological teachers and the official leaders of the churches." [5][source]
This saying of Jesus has caused many people great anxiety throughout the history of the church. Many have wondered if they have committed the unpardonable sin. Concern that one may have committed it is a good indication that one probably has not. The way to avoid committing the unpardonable sin is to believe the testimony that the Holy Spirit has given about Jesus in Scripture, namely, that He is the Christ (i.e, the divine Messiah, cf. 1 John 5:1). [source][source][source]