John Calvin Commentary Exodus 31:18

"And he gave unto Moses, when he had made an end of communing with him upon mount Sinai, the two tables of the testimony, tables of stone, written with the finger of God." — Exodus 31:18 (ASV)

And he gave to Moses. It must be observed that, after the voice of God had been heard from the midst of the fire, and He had delivered the Ten Commandments, and the form of the tabernacle had been described, and the work had been already finished by the craftsmen, though its dedication had not yet taken place, Moses was again withdrawn from the sight and company of men, so that he might be taught privately by himself to be a faithful interpreter of the Law. For although God had briefly contained in the Ten Commandments the sum of His doctrine, which might be sufficient for the rule of a pious and righteous life, yet a clearer explanation was needed, such as Moses afterwards added.

For this purpose he was taken up into the sanctuary (adytum) of heaven, as it were, so that he might intimately learn all things that concerned the full and complete understanding of the Ten Commandments, since he could never have attained their genuine meaning if God had not been his Master and Teacher. From this we gather that he wrote his five books not only under the guidance of the Spirit of God, but as God Himself had suggested them, speaking to him from His own mouth.

Therefore he observed silence for forty days, so that he might afterwards speak freely by the authority of God. Thus all true pastors of the Church ought to be disciples, so as to teach nothing but what they have received.

But although God might in a moment have fully perfected His servant, yet, to demonstrate more surely that he put forward nothing which did not proceed from the school of heaven, he was separated for forty days from the human race, so that the Israelites might from then on look up to him as an angel sent from heaven. For there could be no trace of earthliness about him who had thus lived with God, without food and drink, or any other means of nourishment, and stripped of all weakness of the flesh.

Finally, the Ten Commandments were written on two tables, so that they might never be lost. I have elsewhere stated why they were divided into two tables, namely, because they consist of two parts, the first of which is the rule of piety, while the second prescribes how we must live righteously, innocently, and chastely with men. Thus the worship of God comes first in order, and then the duties of charity follow.

The tables were of stone, since it is usual for enduring monuments to be engraved on brass or stones. That they were written with the finger of God, we must understand to mean that the characters were formed without the hand or skill of men, by the secret power of God. Nor is it surprising that a writing should have suddenly been brought into existence at the same will (nutu) of God, by which the waste and shapeless materials of the world, which they call chaos, were changed so as to be resplendent with astonishing elegance and beauty.

This expression, however, is metaphorical, by which what is only applicable to men is figuratively spoken of God. For God is not corporeal so as to write with His finger, and for Him to act is only to command, as it is said in the Psalms:

He spake, and all things were made; he commanded, and they were created (Psalms 33:9; Psalms 148:5).

Many approve of the allegory, that the Law was written by the Spirit of God on stones, because the hardness of our heart does not receive it without the grace of regeneration. But we must rather hold to the antithesis of Paul, in which he shows that the Gospel differs from the Law in this respect, because it is written on fleshy hearts, subdued to obedience (2 Corinthians 3:3), and indeed it is by no means fitting that we should trifle with such notions as this, when the simple intention of God is abundantly clear, namely, that the Law was recorded on stones, so that the permanence of its doctrine should be maintained in all ages.