Hebrews 10:28

He that despised Moses’ law died without mercy under two or three witnesses:

The law delivered through Moses was God's own law. Contempt for that law brought death without pity on the testimony of two or three witnesses. Those who held it as one or two witnesses teach the same penalty of death without mercy. That penalty stands as the lesser measure, proving that trampling the Son of God, counting the blood of the covenant by which one was set apart as an unholy thing, and insulting the Spirit of grace deserves a far more severe punishment.

The warning reaches those who profess to be Sabbath-keeping Adventists yet continue in sin, especially lustful and impure practices that defile the whole being, and in God's sight such professors are false. Their sinful course works against God and leads others into sin, enticing souls whose consciences are defiled, whose hearts are corrupted, and whose thoughts are continually impure. For them it stands true that vengeance belongs to the Lord, that the Lord will judge His people, and that it is a fearful thing to fall into the hands of the living God.