We're born with lots of built-in traits and tendencies. All human beings have some tendencies towards evil -- some selfish loves. They show up pretty early on. Think "the terrible twos". They stay with us, tenaciously. There's part of our minds, too, that can rise above that selfishness, and ask the Lord for the strength to fight those evil loves. When we do that, we start on the road to Regeneration, or Rebirth.
Changes in our spiritual life are also gradual. They take place one step at a time, and spiritual growth will be easier if we know that it does not take place in a moment. It is an ongoing process.
To change, we must be willing to undergo the temptations described in the Book of Daniel, chapter four, but for this to happen, we need to judge our behavior. This is represented by the feast, where actions are judged and those incompatible with conscience are cast out.
Cain brought an offering of the fruit of the ground, representing the thoughts of our minds. These are indeed from the Lord, for He created them. But they represent only the intellectual part of man; they do not represent the heart. Cain's love was not offered with his gift. There is a lesson here for us.
Here's a summary of the key New Christian teachings about regeneration.