I think many are looking at It this way,The same GOD that spoke In the Old covenant Is the same GOD that spoke the New covenant and since GOD does not change we should try to keep the law and be under grace at the same time.
Some believe that salvation Is by Grace through faith alone but some believe That salvation Is by Grace through faith plus works.
There is certainly misunderstandings. Grace comes "Through Faith". Faith without works is dead. But we all have works. Catholics do Lent and eat fish on Friday. This is their religious tradition. If I see someone following this church tradition, I know what their "Faith" is. We all have faith in something.
But only by Faith in the God of Abraham, which became a man in the person of Jesus and purchased me with His Blood, can we have life.
Part of that Faith must entail trust in His Instructions as the Faith of Abraham shows us.
Abraham believed in God enough to follow His Instructions and the New Testament calls this "Faith".
4 And I will make thy seed to multiply as the stars of heaven, and will give unto thy seed all these countries; and in thy seed shall all the nations of the earth be blessed;
5 Because that Abraham obeyed my voice, and kept my charge, my commandments, my statutes, and my laws.
There have been forces working to deceive people into disobedience since satan used part God's Words to deceive Eve.
We know Jesus said not everyone is saved by His Grace. It would be good if people would do a word study on what "Work iniquity" means. There wouldn't so much division if everyone understood Matt. 7:22.