Jesus was accused of blasphemy because he forgave sins (Matt. 9: 3) which only God could do, and the charge of blasphemy before the Sanhedrin secured a unanimous verdict of guilty (Mark 14: 64) against Jesus, though the ground for this verdict is unclear since verbal abuse of the Temple or a claim to be the Messiah were not themselves blasphemous. Possibly blasphemy lay in a claim to a unique relationship to God, or in ‘leading Israel astray’ (Deut. 13: 5; Ezek. 14: 11).
Blasphemy against the Son of Man, being humiliated and unrecognized for who he was, was forgivable (Luke 12: 10), because his words and deeds could be inadvertently misinterpreted. But blasphemy against the Spirit (an exalted Jesus speaking through the Spirit?) cannot be reconciled with Christian fellowship (Heb. 6: 4–6) and the mutual forgiveness that the Spirit brings.