And Abel, he also brought of the firstlings of his flock and of the fat thereof. Since faith is the result of hearing God's word, and since Abel offered his sacrifice by faith, it is evident that God had told both Cain and Abel what to sacrifice. Abel offered precisely what God had commanded, and did right. Whereas, Cain, through human wisdom, offered a substitute, and did wrong.
Human wisdom is often wrong.
God's way never is. How vain men are who think their ways are equal to God's way. For as the heavens are higher than the earth, so are my ways higher than your ways, and my thoughts than your thoughts. God's way for us is clearly revealed in the New Testament. These things may be done by faith because they are not the products of man's wisdom.