You are most likely right about some, maybe up to "two parts".And for this they think they will receive the "Seal of God," and everyone else will receive the "mark of the beast" and be eternally damned. In short, the fearful thing is that they see their sabbath "observance" as a means of securing their eternal salvation. That should be terrifying for any honest believer who has had a glimpse of his/her own sinfulness and the absolute and perfect holiness of God.
AV Zch 13:8-9 And it shall come to pass, [that] in all the land, saith the LORD, two parts therein shall be cut off [and] die; but the third shall be left therein. 9 And I will bring the third part through the fire, and will refine them as silver is refined, and will try them as gold is tried: they shall call on my name, and I will hear them: I will say, It [is] my people: and they shall say, The LORD [is] my God.
I know what is coming. But GOD promised to help those who are left to go through to the end.
AV Hb 10:29-31 Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified, an unholy thing, and hath done despite unto the Spirit of grace? 30 For we know him that hath said, Vengeance [belongeth] unto me, I will recompense, saith the Lord. And again, The Lord shall judge his people. 31 [It is] a fearful thing to fall into the hands of the living God.
Who gets to call sin, a sin for GOD ???
Who gets to punish for sins against GOD ???
"To be continued...."
Yours in Christ, Michael