Pretty obvious sign of cultish thinking, right? You can be a believer in Christ, live a life of obedience to God, in whatever you do you do to the glory of God...BUT...if you go to church on Sunday instead of Saturday, you are a lawless hell-bound sinner! They pay lip service to grace and throw it back into the face of God.
It’s probably worse than Roman Catholicism. At least others can have a chance with “Purgatory” from their point of view.
I can think of at least 4 instances where The Lord castigated cultist Pharisees for being Sabbath hypocrites. You’d think these people would take a hint?