2. How can the law of God be perpetual and enduring for all people, if it was fulfilled at the cross at the beginning of the new covenant?

The new covenant is older than the old covenant! It was given by God to Adam and Eve in Eden when they failed to obey, and God gave them the promise of the Messiah to come (Genesis 3:15). Israel promised to keep the law of God at Sinai, but unfortunately, they failed to rely on the power of God and instead relied on their own strength. JTL18 4.1

The ancient Jews focused a great deal on the law of Moses, but not in faith, and thus failed to achieve righteousness. While attempting to become righteous through the law, they did not see Christ as the One to whom the law of Moses pointed. JTL18 4.2

The new covenant did not do away with God’s Ten Commandments; rather, Christ’s death on the cross now becomes our motivation for obedience and His holiness becomes ours through faith. Now Jesus provides forgiveness and redemption from sin, writes His law on our hearts, and we delight to do His will by obeying His commandments. JTL18 4.3