Sin, spreading throughout the family of Adam has affected every one born since — except the Lord Jesus. In chapter 3 it was sin against God, here it is murder of another human being. There are many firsts in this chapter (1) the first children; (2) the first offering; (3) the first murder; (4) the first civilization; and (5) the first person who is in the spiritual line to Christ — Seth. The first time we read of worship, we find that it was that which led to the first murder. This shows us that no unsaved person today can worship God. Think of all the blood which has been shed in this world as a result of the first sin.
V.1-17 Cain’s offering was fruit from the ground which God had cursed 3:17. It was bloodless. Abel’s offering pleased God. It is a picture of Christ’s death for us on the cross (Heb. 11:44By faith Abel offered unto God a more excellent sacrifice than Cain, by which he obtained witness that he was righteous, God testifying of his gifts: and by it he being dead yet speaketh. (Hebrews 11:4)). Cain’s and Abel’s altars (in type) are still around us today. Do you see the difference?