If the people are lawless at heart, you can station a policeman on every street corner and you’ll still have crime.
This is why God has devised a new covenant to be written on our hearts and lived out in the world–for everyone to see.
The problem with the Old Covenant was that God’s people couldn’t keep it. Again and again they rallied back around the law, and again and again they fell away from it. So God made a better covenant, and sent His Son to establish it. A covenant of grace. A covenant of the law written not on tables of stone, but on our hearts.
Do God’s laws and God’s grace clash with each other? St. Paul has answered that question.
“Do we then make void the law through faith? God forbid: yea, we establish the law” (Romans 3:31)