Genesis 4:1-5 A More Excellent Sacrifice.
Did Eve hold out hope that Cain was of the seed who would ultimately overcome the serpent? She did acknowledge that the LORD is the one who had provided (v. 1). She also bore Abel. The former tilled the soil, but the latter was a keeper of sheep (v. 2). This bears on the sacrifices which they brought to the LORD. Abel’s was the offering of an innocent sacrificial victim, with the shedding of blood. This was what the LORD required, and no doubt Cain resented that his offering did not suffice, and he would need to go to his brother to obtain an acceptable sacrifice (vv. 3-5). There is some irony that the firstborn of the flock was later given for the redemption of the firstborn of the family (Lev. 18).
That Abel’s was a sacrificial victim is brought out by the fact that it is described as “the firstborn of his flock and of their fat” (v. 4). To eat of the fat was a covenantal curse, so Abel made sure to burn it in the fire (Lev. 7:25). Clearly the sacrificial system was in force long before it was formerly introduced later in all its detail. The writer to the Hebrews in fact states that Abel was regarded as righteous by his faith, that is, he was justified by faith through the offering of the firstborn of His flock. His sacrifice, offered by faith, received the testimony from God that He was righteous (11:4). In this way Abel still speaks to the generations that followed, that the just shall live by faith.