Lieth

4:7 If thou doest well, shalt thou not be accepted? and if thou doest not well, sin lieth at the door. And unto thee shall be his desire, and thou shalt rule over him.

This apparently is God talking.  And, to clarify our doubt from the last verse, he pretty clearly seems to be taunting Cain.  Specifically, he is blaming Cain because God didn't like the offering Cain made, which was pretty much what Cain had to offer.  So how was that Cain's fault?  He should have chosen a different profession, because he should have better offerings.

I have no clue what the last sentence means.  This sounds like the bit from 3:17, where Eve's desire was to Adam and he ruled over her, only inverted.  He's talking to Cain, so it seems like Cain should be doing the ruling.  But it doesn't really make much sense.  Who is the other person?  Abel?  Abel's desire is unto Cain?  That's pretty bizarre, but perhaps it's par for the course for this warped God.