G-d’s prediction and promise to Kayin that he (or any human being) could regain good standing in the eyes of G-d if they complied with G-d’s rules for proper conduct was borne out by the history of the Jewish people.
Rabbeinu Baya Gen. 4:3 Sefaria.org
If we say this, then, the compliance must be that of one who begins with repentance from Adam’s rebellion, which they were born into. The question is, does the history of the Jewsh people being refered to here always begin with repentance from the rebellion of Adam? Even Abraham’s repentance of faith fell short of this briefly when Abraham turned to Hagar.
This was rectified in Isaac and in Jacob. However, the need for this rectification illustrates most clearly what the repentance from Adam’s rebellion is and must be. This repentance is not like that of Kayin offering up agricultural seed, flax seed or otherwise. That is to say, it is not a self-approved gift offering.
It involves an acknowledgement that no self-initiated offering could atone for being heir to Adam’s rebellion. Hevel’s (Able’s) offering, while a gift offering, not being a meal offering that required no death but, being an animal offering and of the firstborn also, which required death and symbolized the death even of the world, was a cry and prayer to God to reveal a justification for life. And Sarah’s womb was the repentance of Hevel, but Hagar’s womb was the self-justification of Kayin.
For Sarah’s womb acknowledged that Hashem alone could decree the blessing of the world in Abraham and his seed. But Hagar’s womb contradicted this acknowledgement, asserting that the blessing of the world could come through one who was not entirely severed from Adam. Not being entirely severed from Adam, Hagar, and Ishmael, the fruit of her womb, was not the representative of the promise of the blessing of the world in Abraham and his seed, which was in contrast to Adam. For Hagar was not called out of Ur of the Chaldees, to leave with Abraham his father’s house, but rather Sarah was called in this way as one with Abraham.
Therefore what Hevel (Able) prayed for by his gift offering Abraham and Mashiach received, the word of G-d for the justification of life. For as the world is blessed in Abraham, so the world is blessed in Mashiach. This word of G-d to Abraham and Mashiach is that which must be acknowledged in order for there to be repentance from being a partaker in the rebellion of Adam against G-d. Only upon this basis can one "regain good standing in the eyes of G-d if they complied with G-d’s rules for proper conduct". For any attempted compliance with G-d's rules which does not build upon God's decree of blessing for the world, (justification for life), through Abraham and Mashiach in contrast to the original blessing and justification for life that came through Adam is, in effect, an assertion that Adam could rebel against G-d and still be the blessing of the world and the justification for the life of the world. Such an assertion is nothing other than a continuation of Adam's rebellion. This false claim is the essence of Kayin's grain offering, which was probably of the poorest grain, but would have been the same no matter what the grain was.