All this came out when Cain and Abel made offerings to Jehovah God. Cain brought fruits and vegetables, whereas Abel “brought some firstlings of his flock, even their fatty pieces. Now while Jehovah was looking with favor upon Abel and his offering, he did not look with any favor upon Cain and upon his offering.” (Gen. 4:3-5) Why? Because Abel had the right heart condition, offered the right sacrifice and offered it in faith, but in all these respects Cain was lacking.​—Heb. 11:4; 1 John 3:12.

Here Jehovah God, in his love and long-suffering, was warning proud, envious Cain about his dangerous heart attitude and telling him that he too could have Jehovah’s favor if he would humble himself by copying Abel’s example. It was an animal sacrifice that was fitting as it involved the shedding of blood, and blood needed to be shed to reconcile man with God.​—Heb. 9:22.