Genesis 4:5-6

Genesis 4:5-6

[5] But unto Cain  and to his offering  he had not respect.  And Cain  was very  wroth,  and his countenance  fell.  [6] And the LORD  said  unto Cain,  Why art thou wroth?  and why is thy countenance  fallen? 

What is the context of Genesis 4:5-6?