You elevate the 10 commandments above the law of Moses because as you say they were written on stone and the rest of his commandments were not. They were written on parchment. Correct? Think about it. The accounts of the LIFE DEATH and RESURRECTION of our Lord were written on parchment as well, which in your mind makes them inferior to the stone tablets. Enough said.
I fail to see the connection between the promise of Christ and our ability, or lack thereof, to keep the Ten Commandments.
Christ was promised to us the moment Adam chose to sin. In fact, the fact that Christ died for £an’s sins only validates the Ten Commandments, not invalidates, because it shows that God could neither change them to make Christ’s sacrifice unnecessary, nor could He remove the punishment that entailed from breaking them.
That is tougher and more permanent than stone, if God Himself cannot change the reality of sin, so you are correct there.
Written in stone means NOTHING! When Moses received the Commandments the people were alredy breaking them. This cause Moses to toss the commandments and they were shattered.
Moses then had to carve two new stones which can just as easily be broken.
Note that the Commandments were placed in the Ark which symbolized death as the Ark was really a coffin for the Commandments.