The Cain and Abel part is his way of dramatizing failed sacrifice versus accepted sacrifice. Abel offers the “firstlings” and “fat,” which Peterson interprets as offering the best thing first, in the right spirit. Cain offers something lesser, then becomes bitter when reality does not reward him as though he had offered his best. Peterson is turning the biblical story into a psychological claim about resentment, self-deception, and the refusal to admit that one’s sacrifices may be inadequate.

The core claim is that if life keeps refusing to open in the way a person wants, one possibility is that the person’s aim or sacrifice is wrong. He is not only saying “try harder,” though it can sound that way. He is saying that bitterness begins when someone secretly knows they are holding something back, then blames God, reality, society, or the successful brother for not accepting the half-offering.

The darker part is his reading of sin as something invited through resentment. Cain’s anger does not stay as disappointment; it becomes hatred of Abel, who represents the living proof that another way is possible. Peterson’s phrase about sin lying at the door means that resentment becomes dangerous when imagination starts feeding it, rehearsing revenge, and turning grievance into identity.

So in plain English, he is talking about how people choose their highest aim, how sacrifice links the present to the future, and how failure can become either correction or resentment. The whole lecture is basically: your aim shapes your world, your sacrifices reveal your aim, and bitterness grows when you refuse to revise the aim or admit the sacrifice was not whole. It is Peterson’s old theme of religious myth as psychological reality, applied to Cain and Abel.

https://www.youtube.com/watch?v=UK1hwJm-l8Q

(http://www.autoadmit.com/thread.php?thread_id=5879323&forum_id=2...id.#49976337)