4 ideas
When the gazelle that nursed Hayy stops moving, he searches her body for the damaged part to fix it. He cuts open her chest and finds the left chamber of the heart empty. He concludes that whatever animated her has left, and that the body was only its instrument, so what he loved was never the flesh.
To test what the human mind can know unaided, remove language, teachers and tradition and keep only a body, an environment and time. Whatever the isolated mind still reaches, from physiology through astronomy to a first cause, counts as available to reason rather than inherited from culture. The method turns an argument about epistemology into a controlled experiment with one variable removed.
Hayy orders his conduct by three tiers of imitation. Like an animal, he gives the body only the minimum it needs, eating ripe fruit and seeds without wiping out any species. Like the heavenly bodies, he acts with purity, orderly motion and care for other living things. Like the Necessary Being, he withdraws into contemplation until the self drops away, and each lower tier serves only to make the higher one possible.
When Hayy meets Absal, he finds that the religion Absal practices describes in symbols and laws the same reality Hayy reached by pure reason. Hayy's attempt to teach the undisguised truth to the people of Absal's island fails and unsettles them. He concludes that most people need the literal parables and rules, so the direct vision should be kept for the few, and he returns to his solitude.