This sin is obviously the only mortal( in Catholic terminology) sin there is. It is spoken of in both Matthew 12:31.32 and is the only sin that can damn the human soul. Jesus
obviously is speaking of it in John 3: 19. Evidence for it seems to me to point to the despising or mocking in your life that which the Holy Spirit has made sacred. Esau
committed it when he sold his birthright. Cf. Genesis 25:34 with Hebrews 12:16,17. Our pathway to our day of repentance and salvation in Jesus involves many decisions along
the road that involve a sensitivity to what is sacred and true. Perhaps lying and deceit are the root causes of our unbelief.
Romans 1:18 says the ungodly .. “hold the truth ( ie supress it) in unrighteousness”. Those who are saved in Christ cannot commit this sin. Romans 8:38, 39 .. more later