So Cain became very angry and his countenance fell. And Cain told Abel his brother. And it came about when they were in the field, that Cain rose up against Abel his brother and killed him. Therefore the key to worship from the beginning, was the attitude of the man's heart. Cain's anger reveals an expectation that his offering ought to have been acceptable to God.
Farmers still think that they work harder than sheep herders.
There, as an outcast woman's question reveals, the mystery of acceptable worship still remained hidden from the gentiles. Your Fathers say that we should worship God in Jerusalem, but our Fathers say on this mountain. I urge you therefore, brethren, by the mercies of God, to present your bodies a living and holy sacrifice, acceptable to God, which is your spiritual service of worship. God welcomes almost any gift at all, from a pure heart. We must not be found in the seat of those who would put themselves between anyone and God.