i do not take away from the rest we have in Jesus.. But just because we have rest in Jesus and are saved by faith in Jesus, do we stop obeying the laws of liberty.
The law of liberty (Law of Christ) in the new testament does not instruct Christians to observe Saturday sabbath.
Jesus said to obey the law. James said to obey the law, Paul said to obey the law and revelation said we should obey. They are all referring to the Ten commandments.
That would be the Law of Christ for us in the new testament.
No matter how you slice it, there are zero instructions in the NT telling us to keep Saturday sabbath because the concept of sabbath is different in the NT than it is in the OT - See Hebrews 4:1-11
If anyone thinks they are required to keep portions of the old testament law in order to earn their salvation then that's what they'll do. It's not what the Lord teaches in the NT but some folk think they are supposed to add to the Gospel by keeping some elements of the OT even though it's not of the Lord.