RAV KOOK ON Breishit Part 2: Cain's Offering

“God did not turn to Cain and his offering; Cain became enraged and his face fell.” (Gen. 4:5) In the story of the world’s first murder, it was God’s decision not to accept Cain’s offering which triggered Cain’s anger and jealousy, ultimately leading to his murder of Abel. Why did God refuse to accept Cain’s offering? What was wrong with it?