John Calvin Commentary Exodus 3:12

"And he said, Certainly I will be with thee; and this shall be the token unto thee, that I have sent thee: when thou hast brought forth the people out of Egypt, ye shall serve God upon this mountain." — Exodus 3:12 (ASV)

And he said, Certainly I will be with thee. It is remarkable that God presents His ready help alone against everything to overcome every fear and to take away every scruple; it is as if to say, it does not matter who Moses is, or what his strength may be, as long as God is his leader. In these words we are taught that we never regard Him with due honor unless, content with His assistance alone, we seek no basis for confidence apart from Him; and, although our own weakness may alarm us, we consider it enough that He is on our side. Hence these celebrated confessions of His saints:

“Yea, though I walk through the valley of the shadow of death, I will fear no evil; for thou art with me.” (Psalms 23:4).

Again,

“In God have I put my trust;
I will not fear what flesh can do unto me.” (Psalms 56:4).

Again,

“I will not be afraid of ten thousands of the people.” (Psalms 3:6).

Again,

“If God be for us, who can be against us?” (Romans 8:31).

Therefore, as we advance in faith, when we are exposed to the greatest dangers, we magnify the power of God. Exalting ourselves in Him, we boldly advance against all the world. This is the basis for firm and tireless obedience, when the thought that God is with us is deeply rooted in our hearts.

But after Moses is commanded to turn his thoughts away from himself and to fix all his attention on the promised help of God, he is confirmed by a sign: that the Israelites would sacrifice on Mount Horeb three days after their departure from Egypt. Still, this promise appears neither fitting nor timely, since it would not actually take effect until the event occurred. I pass over the forced interpretations that some have offered to avoid this absurdity, since others wisely and prudently observe that the confirmation we receive from subsequent signs is neither useless nor futile, and that there are examples of this elsewhere in Scripture.

For example, Samuel, by anointing David, promises that he will be king of the people and pronounces that this will be the sign that the anointing is from God (1 Samuel 16:13). David had to battle with misfortunes for a long time before he could enjoy this sign, yet it will not be considered superfluous, since in its due time it confirmed the favor of God. Similarly, Isaiah, prophesying about the lifting of the city’s siege, adds a sign:

“Ye shall eat this year such as groweth of itself; and the second year that which springeth of the same; and in the third year sow ye and reap, and plant vineyards, and eat the fruit thereof.” (Isaiah 37:30).

It was said to John the Baptist,

“Upon whom thou shalt see the Spirit descending, the same is he which baptizeth with the Holy Ghost.” (John 1:33).

Yet, before John saw that sign, he already knew that Christ was the Son of God, for the prophecies of both his parents were well known to him. But there is nothing absurd in faith that is founded on the Word being increased by the addition of a sign.

In short, God magnifies His mercy by the new mercy that is added, thus, so to speak, heaping up the measure. And, in truth, the calling of Moses was confirmed by a remarkable proof when, in the very place on which he then stood, the people, brought forth through his agency, offered a solemn sacrifice.

In the meantime, God kept His servant in suspense, as if He had said, “Let Me perform what I have decreed; in due time you will know that you were not sent by Me in vain, when you have brought the people safely to this spot.”