Obviously, the closest thing to us is our own life. In a sea of darkness and forgetfulness, it's important that the details of our own human existence are preserved.
The monitoring of earthly lifetimes is the responsibility of powerful spirits who can remember more details of a life than any computer can.
You may come into this world with no memory(i.e.The slate has been made clean.), but you certainly won't leave in the same way.
Other Methods To Preserve Memory