Where does death come from? I know that this is an all together odd question to ask. My response is going to sound even more strange!
As human beings, we seem to crave security above all else. I'm not talking only about physical security--shelter from the elements. We humans seek psychological security--refuge from real or perceived criticism, shame, rejection. We need to know that we are loved and praised, admired, revered.
Death arises out of this pursuit of security. The insecure ego needs to know that it is safe from attacks both inward and outward. Only a permanence of one sort or another will cure the anxiety that accompanies insecurity.
The fact is life is inherently insecure. There is nothing permanent in life, except the fact that everything changes. To free oneself from the misguided pursuit of security is to free oneself from death.