Cain's pride and failure to properly interact with (and receive from) his brother, in order to obtain what was pleasing to the Lord, sent him down the road of jealousy, hatred, and murder.
God's problem with Cain wasn't that he farmed fruits and vegetables instead of livestock. God never suggested an occupational change. He was looking for a heart change that exemplified brotherly love, mutual respect, and interdependence.
Cain, the firstborn, had somewhat of a twisted Messiah complex. He was bent on being a "One-Man-Show" in a human family that required interdependence and a healthy reliance upon "every joint of supply" (See Ephesians 4:16).
Jesus, our one true Messiah and Pattern, exemplifies interdependence upon the Father and the Holy Spirit, along with the rest of His human family! We do well to function in like manner.