There will be no one like us when we are gone, but then there is no one like anyone else, ever. When people die, they cannot be replaced. They leave holes that cannot be filled, for it is the fate — the genetic and neural fate — of every human being to be a unique individual, to find his own path, to live his own life, to die his own death.

-thus Oliver Sacks, via the Laudator Temporis Acti blog.   It is literally true that the graveyards are full of indispensable men.

More than that, every relationship is irreplaceable.  Each part of the trajectory of the relationship is irreplaceable.  Every passing moment is different in some way from all the times before and after.  It is all indispensable.

Which is why, to my mind, belief in the immortality of the soul, the community of the saints, the eternity of the family, and in all things past and present being before His face, are indispensable.  They are psychologically necessities.