Why did God accept Abel's sacrifice and reject Cain's
Thanks for the question. Here are the pertinent scriptures.
And in the process of time it came to pass that Cain brought an offering of the fruit of the ground to Jehovah. Abel also brought of the firstborn of his flock and of their fat. And Jehovah respected Abel and his offering, but He did not respect Cain and his offering. And Cain was very angry, and his countenance fell.
So Jehovah said to Cain, "Why are you angry? And why has your countenance fallen? If you do well, will you not be accepted? And if you do not do well, sin lies at the door. And its desire is for you, but you should rule over it."
By faith Abel offered to God a more excellent sacrifice than Cain, through which he obtained witness that he was righteous, God testifying of his gifts; and through it he, being dead, still speaks.
So, why did God accept Abel's sacrifice and reject Cain's
1.) Simply what the scriptures say, because Abel offered a more excellent or pleasing sacrifice. What made it more pleasing? It was more pleasing because it was the best of what he had, the firstborn and their fat.
Cain just brought some produce. It was not the best that he had. Produce was certainly an acceptable sacrifice since we see that very thing under the Law. But it had to be the firstfruits, the cream of the crop, the very best. What each man brought was not the issue. Cain was a farmer, Abel a shepherd. Rather the issue was the quality of what they brought that concerned God.
Abel brought the best of what he had because he acted in faith. Faith in God, first of all, is that he is, and secondly that he is a rewarder of those who diligently seek him. (Heb. 11:6) Faith will give the best to God. Faith will work the hardest as unto God. Faith will love unconditionally as in the sight of a loving God.
Abel's offering was true worship, the prostration of his heart at the throne of God. He gave himself first and then, the very best that he had. We know he did this because he did it by faith.
2.) There are some that teach that Abel's offering was a lamb which was more pleasing to God than produce because God had commanded a lamb in sacrifice and had not commanded produce from the field as Cain brought. The reason they think this way is because Abel offered his sacrifice by faith. Now since "faith comes by hearing and hearing by the word of God" (Rom. 10:17), therefore Abel must have heard what God commanded to sacrifice and then offered the correct item in obedience.
First, this explanation is reading into the text what is not there. The texts do not say that God commanded anything from the two brothers. This was a time before law. The desire to worship God by these freewill offerings I believe are the natural responses of hearts that fear him and want to serve him. As David said, "nor will I offer burnt offerings to Jehovah my God with that which costs me nothing." (2Sam. 24:24) Besides, the only example we have of God commanding what to sacrifice is under the Law where we find that both kinds of sacrifice were commanded and acceptable.
Secondly, this explanation does a disservice to the idea of what faith is and causes the student to miss this pure and simple example of it. Faith is not simply obedience to commands. Faith is seeing the invisible God as a reality and then approaching him accordingly. This is what Abel did with fear and trembling, being careful not to offend but provide the highest quality gift to the creator. That is the awe and respect that Jehovah deserves. Faith also assumes that God will reward right doing and will bless the righteous. So Abel did what was right to be pleasing to God. This we can assume is "doing well", which Cain was not doing.
I once gave this answer to a Christian in a Bible class on Romans 4, and he said, "Well, I've never heard that before!" I sighed and said, "Yes, I know."
"He that comes to God must believe that he is and that he is a rewarder of those who diligently seek him."
Hope this helps.