Why did God exept Abels sacrifice and not Cains?
Asking for a friend.

Well I always seen it as Cain gave to meet the requirement so to speak and Abel gave the first born of his flock and fat out of true faith in God.

Abel went out of his way to please God which meant he had faith in God. Heb. 11:6, " and without faith it is impossible to please Him, for he who comes to God must believe that He is, and that he is a rewarder of those who seek Him".

Abel's actions were righteous, but Cain's were evil because of his lack of faith. This according to Dallas Seminary Faculty.

Because in order for something to live, something else has to die. Nature even demonstrates this.
Vegans are in denial of this, and not by coincidence, the vast majority of vegans are stringent atheists; at least the ones who I've met.
Cain was acting in rebellion towards God.

This is not in conflict with Matthew 21:28-32?

Cain gave the garbage to GOD, Abel gave the best of what he had

My interpretation, based on the text in the picture below (from the works of Josephus) is that Cain manipulated the ground and did things “by his own will” where able worked within natural systems set up by God. That’s my interpretation based on what Josephus wrote and it makes sense to me

Unless someone has a different scripture verse explaining it, the only thing we know for sure is that it was a faith issue. In Genesis 4, God doesn't really say why Cains offering wasn't right. In Hebrews, we are told Abels offering was by faith. Perhaps Cains was given grudgingly out of duty.

Everyone knows that meat cooking over a fire smells better than burning vegetation. Abel offered some good BBQ, Cain offered burned grass.

Waxing needed?

I do wonder if shedding the blood of the sacrifice made it worthy? Sin offering?

That could be one explanation, another one I have heard is that Cain’s sacrifice was in direct disobedience to God. God commanded them to sacrifice the best lamb of the flock, which Able did and Cain did not.

But in my opinion, it was a faith issue.

Cain offered what grew of its self from the dirt. Abel offered an animal with blood. Part of the justification of a sacrifice was that it had to be equal to what was taken. Certainly fruits from the ground would not equal a man. While an animal was not an equal for the once unblemished Adam before his fall or spirit death, it was symbolic much like the animal skins God clothed Adam and Eve with was symbolic as a future sacrifice so that justice was satisfied (looking forward to) with the sacrifice of The Second Adam (Jesus), which was a perfect sacrifice.

Reciprocal justice was from Exodus 21: 23 And if any mischief follow, then thou shalt give life for life, 24Eye for eye, tooth for tooth, hand for hand, foot for foot

Jasher 1:14-16

"And the boys grew up and their father gave the possession in the land; and Cain was a tiller of the ground, and Abel a keeper of sheep.

And it was at the expiration of a few years, that they brought an approximating offering to the Lord, and Cain brought from the fruit of the ground, and Abel brought from the firstlings of his flock from the fat thereof, and God turned and inclined to Abel and his offering, and a fire came down from the Lord from heaven and consumed it.

And unto Cain and his offering the Lord did not turn, and he did not incline to it, for he had brought from the inferior fruit of the ground before the Lord, and Cain was jealous against his brother Abel on account of this, and he sought a pretext to slay him."

I take this passage as Abel brought the very best and fattest lamb of his flock, but Cain did not bring the very best of his crop to the Lord. I liken it to Luke 21: 1-4.

… probably a green tomato or something

another theory is that God hated cain from the start, as he wasnt of His creation. cain and abel were half brothers of the same mother. she conceived with the devil first, then with adam a short time later. the boys were born in the order in which they were conceived. in the lineage of adam, abel isnt listed as he never procreated, but neither is cain listed, though he DID procreate. just another "something to think about".

Where did Cain find a wife if Adam and Eve were the only humans?

Either a Sister or Niece I'd guess, it was ok then. It's not said but they lived a long time and they had a lot of youngins. Had to be kin though imo.

… the garden of Arkansas

The lineage of Cain and the lineage of Seth is where it gets very confusing for me as their descendants have very similar names. Very difficult to discern them in scripture and determine which is which. That's my case anyway. The Book of Jubilees puts forth a very detailed lineage of both Cain and Seth, but I can't speak for its credibility although, I don't think it should be considered completely irrelevant. Certainly like to hear other views.