And Adam knew Eve his wife; and she conceived, and bare Cain, and said, I have gotten a man from the LORD.And she again bare his brother Abel. And Abel was a keeper of sheep, but Cain was a tiller of the ground. 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.
Hebrews 11:4 tells us that it was by faith that Abel offered a better offering than Cain.
Cain’s offering was not regarded by the Lord, as it is written, without blood there is no remission of sins (Hebrews 9:22). It required blood, in which the Lord said the life of a thing was, in order to atone for the sin of another. And, it was through the eyes of faith that Abel could perceive this. And, for whatever reason, Cain’s lack of faith, or lack of using his faith, was his failure to see.