4 Abel also brought a gift-the best portions of the firstborn lambs from his flock. The Lord accepted Abel and his gift, 5 but he did not accept Cain and his gift. This made Cain very angry, and he looked dejected.
6 "Why are you so angry?" the Lord asked Cain. "Why do you look so dejected? 7 You will be accepted if you do what is right. But if you refuse to do what is right, then watch out! Sin is crouching at the door, eager to control you. But you must subdue it and be its master."
Matthew Henry's Commentary on Genesis 4:4-7
Commentary on Genesis 4:1-7
(Read Genesis 4:1-7)
When Cain was born, Eve said, I have gotten a man from the Lord. Perhaps she thought that this was the promised seed. If so, she was wofully disappointed. Abel signifies vanity: when she thought she had the promised seed in Cain, whose name signifies possession, she was so taken up with him that another son was as vanity to her. Observe, each son had a calling. It is the will of God for every one to have something to do in this world. Parents ought to bring up their children to work. Give them a Bible and a calling, said good Mr. Dod, and God be with them. We may believe that God commanded Adam, after the fall, to shed the blood of innocent animals, and after their death to burn part or the whole of their bodies by fire. Thus that punishment which sinners deserve, even the death of the body, and the wrath of God, of which fire is a well-known emblem, and also the sufferings of Christ, were prefigured. Observe that the religious worship of God is no new invention. It was from the beginning; it is the good old way, Revelation 3:20. And those well deserve to perish in their sins, that will not go to the door to ask for the benefit of this sin-offering. God's acceptance of Abel's offering did not change the birthright, and make it his; why then should Cain be so angry? Sinful heats and disquiets vanish before a strict and fair inquiry into the cause.