An explanation from Calvinist about why Cain's offering is not accepted by God?

This question is following the question before, where Calvin said : > We must, however, notice the order here observed by Moses; for he does > not simply state that the worship which Abel had paid was pleasing to > God, but **he begins with the person of the offerer**; by which he > signifies, that God will regard no works with favor except those the > doer of which is already previously accepted and approved by him The bold sentence from Calvin's quotation above, lead to a conclusion that :
1. God elect Abel before the foundation of the world.
2. He regenerate Abel in time and give him faith, don't know when but before the offering event.
3. Those 2 points above causing Abel do a correct offering.
4. Now God has a reason to look with favor on Abel + his offering.
5. and now God can give him approval as righteous through his offering.
So, *"God begins with the person of the offerer"* as in this case is number 1 and number 2. The logical conclusion about Cain is :
Because God did not elect Cain and God did not regenerate Cain in time and give Cain faith then Cain offering is not accepted by God. *He had no regard for Cain and his offering* as mentioned in Gen 4:5. My question : (according to the Calvinist)
1. What is the cause of Cain's offering is not accepted by God ?
2. Has God regenerated Cain and gave him faith by the time God speak to Cain as read in verse 6 and 7 ?