John Calvin Commentary Exodus 34:1

"And Jehovah said unto Moses, Hew thee two tables of stone like unto the first: and I will write upon the tables the words that were on the first tables, which thou brakest." — Exodus 34:1 (ASV)

And the Lord said unto Moses, Hew thee two tables of stone. Although the renewal of the broken covenant was ratified by this pledge or visible symbol, still, lest His readiness to pardon should produce indifference, God would have some trace of their punishment remain, like a scar that continues after the wound is healed.

In the first tables there had been no intervention of human workmanship, for God had delivered them to Moses engraved by His own secret power. A part of this great dignity is now withdrawn, when Moses is commanded to bring tables polished by the hand of man, on which God might write the Ten Commandments.

Thus the ignominy of their crime was not altogether erased, while nothing was withheld which might be necessary or profitable for their salvation. For nothing was lacking which might be a testimony of God’s grace, or a recommendation of the Law, so that they should receive it with reverence; they were only humbled by this mark, that the stones to which God entrusted His covenant were not fashioned by His hand, nor the produce of the sacred mount.

The fanciful idea by which some interpret it—that the Jews were instructed by this sign that the Law was of no effect, unless they should offer their stony hearts to God for Him to inscribe it upon them—is frivolous; for the authority of Paul rather leads us the other way, where he suitably and faithfully interprets this passage, and compares the Law to a dead and deadly letter, because it was only engraved on tables of stone, whereas the doctrine of salvation requires the fleshy tables of the heart (2 Corinthians 3:3).