We are saying that God's law that was graciously given to Moses in many reasonable ways was temporal. We know that His law was put into effect by an angel through a mediator. But the law that was given to Moses was generously placed in the heart of man. Therefore, those who were naturally born before Moses were equally responsible for breaking the law even tho it wasn't written down.
Since the first Adam failed to properly maintain the law there was a necessary need for a second Adam. Before the law was faithfully executed to Moses God put covenants in place to promptly extend grace to condemned man. He generously provided a sacrifice after Adam sinned. When Adams sin turned into a world wide rebellion God destroyed all mankind except eight righteous persons. After this judgement God made a covenant with Noah that He would no longer judge the created earth and civilized mankind in this arbitrary way.
 Before the giving of the moral law God sufficiently established a eternal covenant with Abram to secure a seed as the number of the luminous stars. This was a grace covenant that generously provided a substitution for breaking the law. The key question , are these covenants eternal? If you carefully look the Abrahamic covenant was part of the eternal covenant that God made to David. These eternal covenants were part of God's plan to satisfactorily establish the infallible rule of David's house over the whole earth. This eternal covenant was proven to be completely implemented in Christ. The question is was God's covenant eternal so that it was planned out in God's eternal counsel before He fashioned the world?

If the covenant undoubtedly remains an eternal one then it was properly provided to work through God's, promises, divine laws, eternal decrees and comprehensive statutes. This means that in order for God's eternal covenants to be comfortably established He had to order all thing through an eternal government. The moral requirements in a covenant agreement had to be divine perfection or there be a unpardonable breach of mutual trust. If there was a ethical breach of betrayed trust then God's lawful government could not be established.

 Consequently, covenant faithfulness had to be absolute. Not only must the law enforcement upheld in every possible situation but its generous provision represent the independent establishment of the most distinguished form of lawful government. So the law not only brought charges to violators but it pronounced death to those who did not rise up to its objective standards. In order for God's government to be established one party in the agreement had to be perfect for there to be real, kindness, long-suffering, and unfailing love. Therefore, God willingly had to satisfactorily complete all the extraordinary work in an eternal way as the highest Governor so that He could establish man through receiving faithfulness, fatherly kindness and eternal love as the appropriate way of success in His eternal government.