John Calvin Commentary Exodus 11:9

"And Jehovah said unto Moses, Pharaoh will not hearken unto you; that my wonders may be multiplied in the land of Egypt." — Exodus 11:9 (ASV)

And the Lord said to Moses. This seems to represent the reason why Moses was so angry; namely, because he had been forewarned that he had to deal with a lost and desperate man. Therefore, when, after so many confrontations, he sees God's dominion despised by the tyrant's audacity and madness, a deeper indignation erupts from him in their final struggle. This is especially because he sees before his eyes that detestable marvel: namely, an earthen vessel so bold as to provoke God with unyielding stubbornness.

But God had foretold to Moses (as we have already seen) the outcome of his great stubbornness, so that Moses, after suffering so many setbacks, would not eventually lose heart. Otherwise, a considerable temptation might have crept in concerning how it could please God to contend in vain with a mortal man. And it was absurd that the hardness of a human heart could not be subdued, corrected, or broken by divine power.

God, therefore, declares that He was in this way planning for His own glory, which He desired to reveal through various miracles. And for this reason, he adds in the next verse that Pharaoh’s heart was again hardened by God Himself. This signifies that the tyrant stubbornly resisted in this way, not without the knowledge and will of God, so that the deliverance might be more wonderful.