What part of Deut 4:2, Deut. 12:8, Deut. 12:32 do they not understand?
Deuteronomy – King of kings' Bible
4:2 Ye shall not ADD unto the word which I command you, neither shall ye diminish [ought] from it, that ye may keep the Commandments of the "I AM" your God which I COMMAND you.
12:8 Ye shall not do after all [the things] that we do here this day, every man whatsoever [is] right in his own eyes.
12:32 What thing soever I command you, observe to do it: thou shalt not add thereto, nor diminish from it.