Why did Hashem not inform Moshe before each plague that Pharaoh would not listen to them?
Rashbam: Although the Torah only records it here, in fact, Hashem informed Moshe before each plague. 1
"Mofsai' is plural. Which plagues was Hashem referring to?
Rashi: He is referring to Makas Bechoros, Keri'as Yam-Suf and the drowning of the Egyptians. 1
Ramban: Hashem was referring to Makas Bechoros (which occurred before Pharaoh sent Yisrael away), and what He meant was that He had hardened his heart against capitulating even in face of Makas Bechoros - in order to increase His wonders (more than all the other plagues), killing man, animals and destroying their gods. 2