The human body is the vehicle that God has provided for the soul to fulfill its task of perfecting itself while in the physical world. As body and soul are partners in this task, the body is also holy and sanctified. Just as a worn-out Torah scroll is still treated with respect because it was a container for holiness (the text of the Torah), so a dead body must be treated with respect because it was also once a container for holiness – the soul. For this reason, Jewish law does not allow cremation. It is a desecration of the person. (This is also the reason for the general prohibition against autopsy.)
There are at least two additional reasons I can think of for a person not to choose to be cremated.
One is that it prevents the fulfillment of a Torah precept to bury a person who has passed from this world. The verse states “You shall surely bury him” (Deut. 21:23). There is a positive mitzvah of burial which cannot be done if there is no body.
In addition, and perhaps most importantly, choosing cremation is denial of the resurrection of the person's body with its soul in the future, which is a fundamental belief of Judaism. I’ve heard from a great Rabbi of the previous generation that a person who chooses cremation will not be resurrected. This fact alone has great permanent consequences for both the person who chooses cremation and very possibly for the person’s descendants.
I hope that your words from your heart penetrate your sister’s heart and that she has a change of heart! May you and your entire family be blessed with long and healthy lives, and much happiness and success.
