John Calvin Commentary Numbers 22:31

"Then Jehovah opened the eyes of Balaam, and he saw the angel of Jehovah standing in the way, with his sword drawn in his hand; and he bowed his head, and fell on his face." — Numbers 22:31 (ASV)

Then the Lord opened the eyes of Balaam. This passage teaches us that, however acute our senses may be, they are not only implanted in us by God but are also either sustained or extinguished by His secret inspiration. Balaam’s eyes are opened; consequently, there was a veil before them previously, which prevented him from seeing what was manifest. Thus God, at His pleasure, dulls the senses of those who seem to themselves to be very acute, since perception is His special gift.

By this example we are shown, as in a mirror, how hypocrites fear God—namely, when they are influenced by His presence; for as soon as they can withdraw themselves, they revel like fugitive slaves. Balaam saw the angel threatening him with a drawn sword, and he hung down his head and adored; that is to say, because the vengeance of God was impending.

But this fear by no means induced him to true self-correction. He confesses, indeed, that he had sinned and puts forth some fruit of repentance in that he is ready to return home; yet he betrays a servile and compulsory fear, which only trembles at the thought of punishment.

I knew not (he says) that thou stoodest in the way. Therefore, unless the Angel had been armed for his punishment, he was proceeding in security, as if impunity were conceded to him.

Another expression also reveals his craft and perfidiousness: he is ready to return if his proceeding should displease God—as if he had not known before that it was by no means pleasing to God. This, then, is a ridiculous condition, as if he were in doubt on a point that was abundantly clear.

If he truly feared God, with pure sincerity of heart, he ought to have at once renounced an expedition that was wicked in itself and improperly undertaken. For of what avail was it to say, I have sinned, if he thinks that he can continue the journey he had begun in opposition to God? Let us, therefore, learn, when God’s will is positively known, to resort to no crooked subterfuges by which we may delay to perform it.

When the Angel says, Unless the ass had turned aside, that he should have slain Balaam without injuring her, he intimates not only that, in accordance with God’s justice and loving-kindness, he would have spared the harmless animal, but also that by the very sagacity of the beast—as though she had deprecated God’s anger—the life of her master, who was otherwise unworthy of mercy, had been redeemed.