John Calvin Commentary Exodus 34:28

"And he was there with Jehovah forty days and forty nights; he did neither eat bread, nor drink water. And he wrote upon the tables the words of the covenant, the ten commandments." — Exodus 34:28 (ASV)

And he was there with the Lord forty days. The number of forty days is repeated so that the second Tablets might have no less credibility than the first; for we have stated that Moses was withdrawn from the common life of men so that he might bring the Law, as it were, from heaven.

If he had only been kept a few days on the mountain, his authority would not have been confirmed by such a conspicuous miracle. But the forty days obtained full credibility for his mission, so that the people might know that he was sent by God, since the endurance of a fast for so long a period exceeded human capacity.

Therefore, so that the majesty of the Law might be undoubted, its minister was endowed with angelic glory. Thus, he expressly records that he neither ate bread nor drank water, since it was necessary that he should be distinguished from other mortals, so that his official role might be unquestionable.

Now, it must be remembered that this was not a mere fast of temperance or sobriety, but of special privilege, by which exemption from the weakness of the flesh was granted to Moses for a time, so that his condition might be different from the rest of the human race.

For he neither felt any hunger, nor did he struggle with any longing for food, nor did he desire food and drink any more than one of the angels.

Therefore, this instance of abstinence was never cited as an example by the Prophets, nor did anyone attempt to imitate what they all knew was by no means granted to them.

I make an exception for Elijah, who, being sent to revive the Law when it was almost lost, like a second Moses, also abstained from eating and drinking for forty days.

The reason for Christ's fast was similar (Matthew 4:2), for, in order to acquire full credibility for His Gospel, He desired to make it clear that He was by no means inferior to Moses in this respect.

Therefore, ³⁸⁸ that error is the less excusable, which arose from gross ignorance, when all, without exception, tried to rival the Son of God in their annual fast, as if a new proclamation of the Gospel was entrusted to them. For Christ neither fasted forty days more than once in His life, nor during that entire time, as is clearly specified, did He experience hunger. And His heavenly Father separated Him from the company of men when He was preparing Himself to undertake the role of teacher.

³⁸⁸ For a fuller development of this argument, see Institutes, Book 4, chap. 12, sec. 20, 21; and Harm. of the Evangelists, vol. 1, p. 208. Calvin Soc. edit.. Calvin Soc. edit.