The unpardonable sin, or blasphemy against the Holy Spirit, is the knowing, hardened, final repudiation of the Spirit’s recognized testimony to Christ.
When Jesus’ enemies attributed His Spirit-wrought works to the devil, He warned of a blasphemy that shall not be forgiven. This is not a single hasty word or a sin of weakness that troubles a tender conscience; it is the settled, clear-eyed rejection of the very Spirit who testifies of Christ — a hardening so complete that repentance is no longer sought.
The warnings of Hebrews 6 and 10 correspond closely, though Scripture does not explicitly say they define the identical sin. The anxious are not its subjects: the person who fears he has committed it shows the very tenderness it lacks.
See in Scripture: Matthew 12:31–32; Mark 3:28–30; Hebrews 6:4–6; Hebrews 10:26–29