☦ Eastern Orthodoxy: Grave sin clamoring unto Heaven.
[Repeated hardened resistance to the calling/encouraging of the Spirit to repentance is serious and dangerous to one's mortal soul. A feature/ploy of the Enemy to deceive. Yes, comes into play the person's formative years to present 'adult' stage. A 'certain person' in our daily consciousness is plagued by deception. God help us quickly.]
Jesus Christ called the Holy Spirit "Spirit of Truth" (John 14:17; 15:26; 16:13) and warned us, "All manner of sin and blasphemy shall be forgiven unto men; but the blasphemy against the Holy Spirit shall not be forgiven unto men" (Matthew 12:31).
"Blasphemy against the Holy Spirit" is conscious and hardened opposition to the truth, "because the Spirit is truth" (1 John 5:6). Conscious and hardened resistance to the truth leads man away from humility and repentance, and without repentance there can be no forgiveness. That is why the sin of blasphemy against the Spirit cannot be forgiven, since one who does not acknowledge his sin does not seek to have it forgiven.
—?Serafim Alexivich Slobodskoy, The Eighth Article of the Creed
Attribution: Wikipedia