One of the ways that the Torah or instruction of God can be shown to be eternal is by taking a step back and looking at patterns and principles that are prevalent in both of the old covenant and the new covenant.
Was a covenant with the one true God
Had a high priest and a king
Had blood ratification and sacrifice
Had a temple
Had a kingdom and a land
Inclusion evidenced by circumcision
Surprisingly, the new covenant contains the same principles:
Is a covenant with the one true God
Has a high priest and a king (Yeshua)
Has blood ratification and sacrifice (once-for-all through Yeshua)
Has a temple (the body of believers in whom God dwells)
Has a kingdom and a land (the world)
Inclusion evidenced by circumcision (of the heart)
Looking at the similarity of these principles, it becomes evident that Torah surpasses covenantal ages and is eternal.