Chandler is stating that the two seeds are literally from Adam and from Satan (lucifer). But Lucifer was a spiritual being, and could not impregnate with a material seed.

Genesis 4 is quite clear. Adam made love to Eve, and she conceived Cain. Later, she conceived Abel.

Cain and Abel are BOTH the offspring of Adam. BUT the problem is, Adam was fallen, and under Lucifer's dominion. Through the fall, Adam inherited evil nature from Satan. but he still had good nature from God.

God cannot relate to an evil being, as God is not evil. So God had to symbolically divide the good part of Adam from the evil part of Adam. He did this by symbolically setting up Cain as symbolizing the evil aspect of Adam, and Abel as symbolizing the good or Godly nature in Adam.

Also, Cain, as the first born, symbolized the first fallen union by Eve - that with Lucifer, which was 100% wrong. Abel as the second born, symbolized the second fallen union, of Eve with Adam. (this was also evil, because it was motivated by Eve's fallen fear inherited from Satan, and not achieved under God's blessing. But because Adam was originally intended to be Eve's spouse, this fallen union was less evil than the first.)

So Cain was in a position to relate to Satan as his master and subject, and Abel in a position to related to God as his master and subject.

This is why God had the two sons now make an offering. He received Abel's, because Abel was in that position, but rejected Cain's because Cain was in that other position. For what purpose?

To reverse the fall of humanity. Lucifer (created before Adam i.e. 'first born') could not humble himself to Adam (created after Lucifer, i.e. 'second born') but instead killed him. If Cain could humble himself to Abel, and unite with him, it would symbolize the reversal of Lucifer's mistake. On that foundation, God could send the messiah.

What did God say to Cain, when he got upset? "If you do what is right, will you not be accepted? But if you refuse to do what is right, sin is crouching at your door; it desires you, but you must master it.”

In other words, what was 'right' for Cain to do was to humble himself to Abel, and ask Abel's assistance in making the offering in the right way. but instead of REVERSING the mistake of Lucifer, Cain actually repeated it, and murdered his brother who symbolized Adam.

It becomes clear that this is a n accurate interpretation when you read the scripture in the old and new testaments. Constantly, God was setting up elder brothers to be challenged by hate towards their younger brothers, so that by overcoming that, the fall of Lucifer if spiritually murdering Adam could be reversed as the start of the lineage that could bring the Messiah.

Shem ham and Japeth in Noah's family. (Ham was 'abel' but he failed to have faith in his father, and actually brought a curse on the family.) Abrham's sons, Ismael (elder) and Isaac (younger). Isaac's sons, Esau (elder) and Jacob (younger). The sons of Joseph, Manasseh and Ephraim.

The difference is, Jacob through humbling and loving Esau after many years of tribulation (21 years in Haran), actually melted Esau's heart, and Esau embraced Jacob instead of murdering him. THIS is exactly why Jacob was the start of Israel, and the head of the lineage that Jesus would be born from. A lineage of the one who successfully symbolically reversed the fall of Adam to Lucifer.