Q. Why does Judaism believe dead bodies cause defilement?
The deceased separates into body and soul. The body has done its work and is laid to rest. The soul is eternal and enjoys the spiritual bliss of life with God. In that spiritual realm there is no defilement; defilement has meaning only on earth.
As far as the survivors are concerned, the body, now separated from its soul, cannot be allowed to remain amongst us as if it still had work to do.
I have known people who wanted to keep the body of their dead at home as if to pretend that a loved one could still participate in earthly life. Jewish tradition insists on the opposite, that there must be closure. Hard though it is, the body must be laid to rest and the soul must move to its new sphere.
We must reject the conventional translation of the Hebrew tamei as “unclean”; this is a misreading of the texts and suggests wrongly that there is something physically dirty about the body.