Genesis 4:3-7 In the course of time Cain brought some of the fruits of the soil as an offering to the LORD. 4 But Abel brought fat portions from some of the firstborn of his flock. The LORD looked with favour on Abel and his offering,
5 but on Cain and his offering he did not look with favour. So Cain was very angry, and his face was downcast. 6 Then the LORD said to Cain, "Why are you angry? Why is your face downcast?
7 If you do what is right, will you not be accepted? But if you do not do what is right, sin is crouching at your door; it desires to have you, but you must master it." (NIV)
Cain and Abel somehow knew about the need to bring an offering to the Lord. Genesis chapter 4 tells us that God respected (or accepted) Abel's blood offering (or sacrifice) but not Cain's. God also told Cain that he did not do what was right (verse 7).
From the above facts we can safely deduct that Cain and Abel knew about the need to offer a sacrifice to God. They were also aware of the right way to do it. Notice that it was Cain and his offering that God disapproved of.
Cain was knowingly doing something wrong. Considering the fact that Abel's sacrifice was accepted by God and in the light of Genesis 3:21, it seems apparent that the right offering (or sacrifice) was the blood sacrifice.
Cain for some reason refused to offer the right sacrifice. God actually told Cain (verse 7) that if he had done "what is right" his offering would have been accepted. Abel's offering was right and it was accepted
Our fellowship with God is based on the blood of the Lamb of God slain from the creation of the world. The lamb is the ?right? and ?only? sacrifice acceptable to God. The account of Cain and Abel sheds light on this fact.
Cain rejected the blood and allowed sin to dominate him. A fact that is still valid today. When we refuse to accept the power and authority of the blood, either knowingly or ignorantly, we open the door to satan and sin.
Cain went on to kill Abel and from that event we can learn another truth about the blood.