@Shaolin
Your reference did not say Abel was sent to Cain to give him a message. If you wish to infer, God spoke to Cain & warned Cain, but whatever he had talked about in the field was hardly anything God told Cain to tell Abel about.
The irony is on what God had told Cain that Abel's desire is to Cain and that Cain would rule over Abel. Cain was the first born anyway.
As for Abel being a half breed, there is no scriptural basis for that as being of the truth.
Genesis 4:1And Adam knew Eve his wife; and she conceived, and bare Cain, and said, I have gotten a man from the Lord. 2 And she again bare his brother Abel. And Abel was a keeper of sheep, but Cain was a tiller of the ground.
There were no other people on earth when Cain was born first and Abel was born second.
Genesis 3:20 And Adam called his wife's name Eve; because she was the mother of all living.
There were other children by Adam & Eve after Cain & Abel for how, after many generations, Cain was able to find a wife which was a relative of his at the time he had murdered Abel. That was why there was no place for him to go on earth for every one was related to Abel and Cain, but would take vengeance on Cain for killing Abel..
The sons of God are the godly lineage of Seth that had replaced Abel, whom had died. The sons of God is a reference only pertaining to Israel's family tree.
Luke 3:38 Which was the son of Enos,
which was the son of Seth, which was the son of Adam, which was the son of God.
Now Christians are the sons of God not by blood lineage nor by Judaism.
John 1:12 But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name: 13 Which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God.