John Calvin Commentary Numbers 22:35

"And the angel of Jehovah said unto Balaam, Go with the men; but only the word that I shall speak unto thee, that thou shalt speak. So Balaam went with the princes of Balak." — Numbers 22:35 (ASV)

And the angel of the Lord said to Balaam.

Again, this wicked man is ironically permitted to do what could not be carried out without sin. But, as I have said before, he was so conscious of his ungodly covetousness that he knowingly and willfully deceived himself, instead of being deceived.

At the same time, we must observe that, as Paul calls God’s wisdom “manifold,” (Ephesians 3:10), so His will is declared in various ways, as if He were inconsistent with Himself, though it always actually remains the same.

It is certain that it was a mere pretense on Balaam's part that he went at the command or permission of God. Nevertheless, this answer was given him, “Go,” etc. God, indeed, cast derision on the stubborn folly of this wicked man and did not approve as proper what, as far as words went, He permitted. Meanwhile, these two things are consistent with each other: that God did not approve what He condemned, and yet chose that it should be done.

For, even when He executes His purpose by means of wicked men, He does not prescribe to them that they are to act thus. He willed to exact punishment from Solomon by the hands of Jeroboam, and that the impiety of the house of Ahab should have vengeance inflicted upon it by Jehu. Still, it was not right for Jeroboam to upset what God had declared, that is, that the posterity of David should continue upon the throne. Jehu also, although he had been anointed by the Prophet, was still guilty of a criminal act in seizing the kingdom, inasmuch as nothing but ambition impelled him to it.

Regarding the history before us, it was His will to prove by the mouth of Balaam how effectual and unchangeable His determination was concerning the adoption of the people, by which His truth and faithfulness might be more conspicuously shown forth. Nevertheless, Balaam sinned, because he was attracted, like a hound, by the scent of gain, to sell his curses for money.