And whosoever speaketh a word against the Son of man, it shall be forgiven him: but whosoever speaketh against the Holy Ghost, it shall not be forgiven him, neither in this world, neither in the world to come.
— Matthew 12:32 —
Mark 3:29 But he that shall blaspheme against the Holy Ghost hath never forgiveness, but is in danger of eternal damnation:
Matthew 12:30-32 He that is not with me is against me; and he that gathereth not with me scattereth abroad. 31Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy against the Holy Ghost shall not be forgiven unto men. 32And whosoever speaketh a word against the Son of man, it shall be forgiven him: but whosoever speaketh against the Holy Ghost, it shall not be forgiven him, neither in this world, neither in the world to come.
Luke 12:8-12 states,
8Also I say unto you, Whosoever shall confess me before men, him shall the Son of man also confess before the angels of God: 9But he that denieth me before men shall be denied before the angels of God. 10And whosoever shall speak a word against the Son of man, it shall be forgiven him: but unto him that blasphemeth against the Holy Ghost it shall not be forgiven. 11And when they bring you unto the synagogues, and unto magistrates, and powers, take ye no thought how or what thing ye shall answer, or what ye shall say: 12For the Holy Ghost shall teach you in the same hour what ye ought to say.
You must witness to others what you learn from the Holy Spirit. If you are ashamed to confess your faith in Christ, you will not be forgiven. If you fear being ostracized for being different, you will not receive forgiveness. If you deny Christ as Peter denied Christ, you will not be forgiven. In order to have committed this sin, you must first have received the Holy Spirit. Hebrews says,
Hebrews 6:4-6 For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, 5And have tasted the good word of God, and the powers of the world to come, 6If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.
Falling away or being an unprofitable Christian after you receive the Holy Spirit is the “blasphemy against the Holy Ghost” (the unforgiven sin). Peter had not yet received the Holy Spirit at the time he denied knowing Christ (John 7:39). Peter denied Christ three times. Christ allowed him to take it back three times.