Thanks for post this discussion on kamma. I think that once a person understands what the suttas reveal about what kamma is, what the Buddha discovered about rebirth and how kamma works will not only clear up questions about kamma but will help one to see the Noble Eightfold Path much more cohesively.
This is a complex question to answer in a post! In a very brief synopsis, here’s how I understand it to work. I’m open to correction!
First, a little backstory to know what’s happening in the mind.
Consciousness is one of the 5 Aggregates of grasping. Consciousness is impermanent: a constantly changing process, an ever changing flux of states of consciousness. SN 22.95
Ajahn Brahm has said that if we want to know what consciousness is, we need to know what it does. Ven. Sujato has defined consciousness as "the faculty of knowing, stimulated by the 6 senses.”
In MN 43 we learn that an unwise person feels and cognizes/knows, but doesn’t understand the Four Noble Truths of suffering, thus makes bad choices. They are fooled by the magic trick that internalizes and believes that consciousness is a self/soul/permanent entity when it is actually impermanent, a constantly changing stream of consciousness.
A wise person understands the Four Noble Truths of suffering. With wisdom, the mind understands what it cognizes/knows and cognizes/knows what it understands.
The mind inclines towards what it thinks about frequently and its underlying tendencies. SN 12.40
Through AN 10.104 we understand that an unwise person thinks frequently about sense pleasures, anger, cruelty etc., and willfully acts with bad deeds. Consciousness with those underlying tendencies is established as a field where the seeds of bad intentional deeds are planted and moistened by craving. When that person dies, the field does not die, but rather, the stream of consciousness with its field of kamma and its craving is planted like a seed into the next life, continuing on. Rebirth.
The memory that is lost upon death is the identification with the previous life. In rebirth, the seeds of intentional action of the stream of consciousness (kamma) continues growing and operating in a new life and the vipaka (ripening of that kamma) of previous deeds continues on.
It wasn’t until the Buddha had purified his mind spotlessly was he able to discern rebirth directly. That’s why it so important and rewarding to follow the Dhamma, develop wisdom, understand the Four Noble Truths, remove the impurities of the mind, and make good kamma.
There is no storehouse of kamma and there is no entity or force of the universe enforcing vipaka. A person is the heir to their deeds and it’s up to them to purify the mind and think and act with Right Action.