Genesis 4:3-5

"And in process of time it came to pass that Cain brought of the fruit of the ground an offering unto Jehovah. And Abel, he also brought of the firstlings of his flock and of the fat thereof, and Jehovah had respect unto Abel and to his offering: but unto Cain and to his offering he had not respect. And Cain was very wroth, and his countenance fell."

"In process of time ..." is an expression that moves this episode to a point long after the events of the preceding chapter.

"Fruit of the ground ... firstlings of his flock ..." The reluctance of present-day exegetes to find the reason for God's displeasure with Cain's offering is due solely to their failure to read the event in the light of N.T. revelation concerning it. Hebrews 11:4 categorically states the reason for the acceptability of Abel's sacrifice as being solely due to his having offered it "by faith," a truth which emphatically declares that he offered in harmony with what God had commanded him to offer. The denial that the institution of sacrifice existed at this early time is a gross error. Could it possibly be supposed that these two brothers spontaneously, voluntarily, and simultaneously decided to honor God with a sacrifice at a time when the instruction was unknown and in the absence of any divine regulations whatever concerning such things? How impossible is such a thing even to be imagined. The N.T. reveals "The Lamb slain from the foundation of the World," (Revelation 13:8, KJV), and there can hardly be any doubt that the offering of a lamb as a sacrifice also dated from the foundation of the world - a truth attested both by type and antitype. Of course, after the intervening millenniums of time, we may easily see why the "firstlings of the flock" pleased God. But, of course, Cain and Abel could not know the future; and their only guide to pleasing God was to do what God had commanded, exactly the thing that Cain did not do.

Having missed the true explanation of this, many of the commentators demonstrate their error by advancing all kinds of contradictory reasons for God's rejecting Cain's offering; "Cain's heart was no more pure,"[9] "He resented having to accept God's Lordship,"[10] Cain's offering was "stinted," and Abel's "unstinted,"[11] "Cain offered ... merely to keep on good terms with God!"[12] Some even allege that it was the "disposition" of the two brothers that made the difference. All such explanations of why God rejected Cain's offering are absolutely unsupported by the text. The evil attitude of Cain did not appear until after his offering was rejected. The amount, or value, of either sacrifice is not even mentioned, nor is there any evidence whatever that Cain resented God's Lordship. John Skinner referred to all such explanations as "arbitrary," and identified God's displeasure as resulting from "the material" of Cain's sacrifice "not in accordance with primitive Semitic ideas of sacrifice."[13] This of course is true, provided that it is also understood that those primitive Semitic ideas of sacrifice had been specifically conveyed to them by the Almighty. Only by this could it possibly be said that Abel's faith enabled the "more excellent sacrifice." Here again is an example of how the man-made rules of the seminarians sometimes throttle their minds and make it impossible for them to see the truth.

There are many things which we do not know about this episode, one of them being how the brothers knew that God had accepted one sacrifice and rejected the other. Speculation is vain; we still do not know.