He died that day because his body had served its purpose. His soul had done what it came to do, learned what it came to learn, and then was free to leave.
Learning does not make one learned: there are those who have knowledge and those who have understanding. The first requires memory and the second philosophy.
This is my simple religion. There is no need for temples; no need for complicated philosophy. Our own brain, our own heart is our temple; the philosophy is kindness.