Offering

4:3 And in process of time it came to pass, that Cain brought of the fruit of the ground an offering unto the LORD.

I don't understand the whole concept of offerings to God.  Apparently I'm not alone; the practice seems to have died out.  Cain's giving God food because God's hungry?  Because God is wildly insecure and needs gifts to feel good about himself?

And Cain is grateful to God because God made farming difficult?  Because God made snakes bite Cain's heels?

The open phrase is a very windy version of "eventually".  But it wasn't necessary to point out the passage of time between Cain and Abel being born and them getting occupations.