Cain was labouring with the earth (five senses, subjective reasoning), and God always rejected his offerings. What were these offerings?
And Cain said unto Jehovah Elohim, My punishment (that is the subjective reasoning) is greater than I can bear.
Behold, thou hast driven me out this day from the face of the (Edenic) earth; and from thy face shall I be hid (within the Intellect); and I shall be a fugitive and a vagabond in the earth (Physical Body); and it shall come to pass, that every one that finds me (through meditation) shall slay me.
And Jehovah Elohim said unto him, (it wont be so easy) therefore whosoever slays Cain, vengeance shall be taken on him sevenfold (he will pay the karma of his seven capital sins). – Genesis: 4:13,15
The mind is the den of the ego. The ego is seven, the ego is mind, Cain is mind, the seven capital sins.