John Calvin on Exodus 34:3-4

3. And no man shall come up with thee Again men as well as beasts are prohibited from access to the mount, as had been the case at the first promulgation of the Law, in order that the people might obediently receive the Law as if come down from heaven. Why God admitted no witness, is a question the answer to which must remain with God Himself. The miracle indeed would have been illustrious if the writing had appeared in a moment on the empty tables; but God would leave some room for faith, when He employed the intermediate agency of man. But still He amply provided what was sufficient to establish the dignity of the Law, when Moses brought the Ten Commandments written upon two tables which the people had lately seen taken up void and empty, whereas He could not have found in the mount a chisel or graving-tool. For “Voyla comment Dieu dispense par bon moyen le cognoissance de sa Parole;” Behold how God dispenses in a good way the knowledge of His Word. — Fr. God so administers the dispensation of His heavenly doctrine as to prove the obedience and teachableness of believers, whilst He leaves no room for doubting.