To answer your good question, let’s read Genesis 4:3-7, “And in process of time it came to pass, that Cain brought of the fruit of the ground an offering unto the LORD. And Abel, he also brought of the firstlings of his flock and of the fat thereof. And the LORD 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. And the LORD said unto Cain, Why art thou wroth? and why is thy countenance fallen? If thou doest well, shalt thou not be accepted? and if thou doest not well, sin lieth at the door. And unto thee shall be his desire, and thou shalt rule over him.”

Adam and Eve had sinned and had been cast out of the Garden of Eden. We don’t know how much later, but after been cast from the Garden, they had two sons: Cain and Abel. In due time, it was proper for Cain and Abel to sacrifice to the Lord, both as an acknowledgement of God’s holiness and their own sinfulness. We can reasonably assume that the sons of Adam and Eve had witnessed their parents making sacrifices to the Lord. So, Cain, the farmer, brought the Lord the fruit of the ground. Abel, the shepherd, brought the Lord the firstborn of his flock. As we just read, “the LORD had respect unto Abel and to his offering: But unto Cain and to his offering he had not respect”. What happens next reveals the true character of Cain’s heart.

Instead of bowing his will to the will of God, Cain becomes angry. This shows us that Cain did not have a true heart that realized the absolute holiness of the Lord. He offered to the Lord according to his own will, and when that was rejected, we see no repentance in Cain, only anger. Hebrews 11:4 says, “By faith Abel offered unto God a more excellent sacrifice than Cain, by which he obtained witness that he was righteous…” It was by faith that Abel sacrificed to the Lord according to the will of the Lord. This is not said of Cain.

The Lord’s reaction to the anger of Cain illustrates His own great love and patience towards Cain. Let’s read the words of the Lord to Cain in Genesis 4:7 from the Young’s Literal Translation for better clarity. That says, “Is there not, if thou dost well, acceptance? and if thou dost not well, at the opening a sin-offering is crouching, and unto thee its desire, and thou rulest over it.” The Lord assures Cain that if he would act correctly, repent of his sin and offer to the Lord according to His will, He would accept Cain’s sacrifice. The word ‘sin’ in the Old Testament is sometimes translated, and understood to represent a ‘sin-offering’. One example is found in Exodus 29:14, “But the flesh of the bullock, and his skin, and his dung, shalt thou burn with fire without the camp: it is a sin offering.” This is the same Hebrew word translated ‘sin’ in Genesis 4:7.

In His wondrous grace, the Lord provided Cain with an animal that he could take and sacrifice to the Lord. He even brought it to the door of Cain’s tent. What grace! We understand this wondrous grace of God in verses like Romans 5:20 which says, “…where sin abounded, grace did much more abound.” Sadly, the character of Cain’s heart was revealed even further when he killed his brother and then lied to the Lord about it. (163.8)