Why did Christ take the place of the sinful son of Israel?
Christ took the sinful son of Israel's place so God could lay the curse of the Law on Him. He became the curse under God and fulfilled all the Law's curse, so God could forgive, reconcile, and pardon every human being who will simply believe.
Les explains that the horrible, worst imaginable sins the human race can commit—the most vile sin man could imagine—were all laid on Christ. He took the place of that rebel, sinful son of Israel so God could put the curse of the Law on Him. Christ became the curse under God and fulfilled all the curse of the Law, so that God could now say He has forgiven, reconciled, and pardoned every human being. It is there for anyone and everyone who will simply believe. Les notes this is strong language many do not like to hear, but it is what the Word declares. The context then points back to Romans chapter 3 and Paul's plan of salvation, where keeping the Law brings no justification.
Christ hath redeemed us from the curse of the law, being made a curse for us: for it is written, Cursed is every one that hangeth on a tree: