Matthew Poole and continuators on Genesis 4:5

5. But unto Cain and to his offering he had not respect: And Cain was very wroth , and his countenance fell .

Partly with God, who had cast so publick a disgrace upon him, and given the preference to his younger Brother: And partly with Abel, because he had received more Honour from God, and therefore was likely to have more respect, and priviledge from his Parents than himself.

Whereas before it was lifted up and chearful, now it fell down through sense of guilt, disappointment of his hope, shame, and grief, and envy at his Brother.